Parabens, Skincare, Safety, and Cancer: What does the Science say?

Parabens - are they safe or not? You've seen them in ingredients lists - methylparaben, ethylparaben, propylparaben, and butylparaben are the most commonly used ones in cosmetics and skincare, but there are a bunch of others, such as isobutylparaben, isopropylparaben, benzylparaben and so on. You've also probably heard that they are unsafe, and can cause cancer (in particular breast cancer) because they are endocrine disruptors. But are they really unsafe? What does the science say, beyond the hype? I've actually touched on the topic before, but it was in the comments section of this post from last year, in response to a reader's question about parabens in cosmetics. Although I had initially intended to only answer that reader's question (yes, that super long 4-comments-long answer was just for one reader), I seem to get hits for "parabens" leading to that post. Since the main body of that post is actually a skincare review, and people may not read the comments, I thought it would be good for me to create a separate post for it, so that it is easier for them to access the information directly without having to scroll through all the comments. I've also expanded my responses, since now I'm no longer constrained by Blogger's comment length limit - take that, Blogger comments!

Parabens - safe or not? Given the rage on the Internetz, you'd think they were a major source of slow, painful deaths.

So. let's cut to the chase. The original reader comment was as follows:
"I...was wondering whether you knew more about the parabens controversy. I've always wondered if all parabens are cancerous and bad for you, or is that just misinformation. Is there a reason why beauty products use them so often, maybe for certain properties and purposes it serves?"

So there are actually three broad parts to this question:
1. Are parabens safe?
2. If they are safe, why are they so controversial? Where does the hype come from?
3. If there is so much hype about them being bad, why are they still commonly used?

Molecular structure of some common parabens (Image source)

With that, I thought this post would provide a more systematic way of answering these questions, and gathering all my sources in one place, so those three questions are how I will tackle the question. I've definitely heard all about the paraben controversy, and to be honest, I've found there is quite a bit of misinformation, half-truths, and fearmongering out there. The truth is, if you look at the amount if hoopla online in certain parts of the Internetz, versus the actual scientific data on parabens, you'll find that there is very little to justify the hoopla. But enough of my talking - let's dive into the analysis now! Just be warned: this is a very, very long post, so you better buckle yourself in!

1. Are parabens safe? Who decides whether they are safe or not?

A. What are parabens? What does the safety data say?

First, a quick introduction to what parabens are. Parabens are preservatives that are added to cosmetic products to prevent microbial growth, which most commonly happens after a product is opened and the consumer starts using it (because when you open a jar of cream and stick your fingers in it, germs and other forms of life can get inside and start to breed). The level of preservatives used in cosmetic and skincare products is usually less than 1%, and in most cases the typical usage is at levels 0.01 to 0.3%. Parabens are also allowed for use in food, also in limited amounts as an additive, and they do occur naturally in fruits and produce like grapes, blueberries, and so on. But it's just a little tidbit of extra info - I won't go too much into parabens in food because this is a beauty blog, but just know they exist naturally in some foods and are allowed in limited amounts too.

Parabens can be found occuring naturally in blueberries, grapes, and other foods we eat. (Image source)

Now that we've established what parabens are, what does the existing scientific data say about them? Here is where we really cut through the hype. Contrary to some of the really aggressive misinformed opinions out there on the Internetz, parabens actually have a good track record of safety as far as their use in cosmetics is concerned. And while some people like to claim there "isn't enough information on whether they are safe", that's not really true - parabens actually leave a trail of documentation stretching back to the 1980s, before I was born.

The US Cosmetic Ingredient Review (CIR) first reviewed parabens and determined that they were safe for use in 1984, and subsequently, perhaps due to all the hoopla out there, has actually reviewed the safety of parabens a number of times (including in 2003, 2005, 2008, 2011 and 2012), and each time the conclusion is that parabens are safe.

B. Wait, what is the CIR? I read on the internetz that it's funded by the industry - doesn't this make it unreliable?

For those who don't know what it is, the US CIR is an industry-sponsored organization that reviews cosmetic ingredient safety and publishes its results in open, peer-reviewed literature. FDA participates in the CIR in a non-voting capacity. Some people (primarily the sites with "our cosmetics are killing us"-type views), like to discredit the CIR, because it is an industry-sponsored organization - in effect, it's expecting the industry to regulate itself. While it is true that the CIR is funded by the industry, I still find that their methods are very fair and transparent. Basically what the CIR does is:
1) Look at all the available scientific studies on the ingredient they're reviewing,
2) Assemble a panel of experts (called the CIR Expert Panel) to have a meeting (CIR Expert Panel Meeting) to look at the studies and discuss whether, given the data available, it is safe to use. These meetings are pretty long, and can take a couple of days. The CIR Expert Panel consists of a good variety of qualified people - there are doctors of course, but doctors don't know everything about formulating skincare, so there are also people with more specific relevant technical fields like toxicology, medical chemistry, pharmacology, chemistry, and so on. And everyone on the panel has a PhD. And their names and designations are all given - so you know who is on the panel.
3) Then, a month or so after the meeting, they publish various documents from the meetings on the CIR website. These documents are public for everyone to read. These include: the final safety reports on the ingredients discussed, the tentative reports, which are released before the final report is ready (these two are the documents that I refer to the most to see safety data), the minutes of the meeting, the transcripts of the meeting (those are fun to read but very, very long because each meeting is like 2 days - you can take a look at the transcripts of a recent December 2013 CIR Expert Panel Meeting here), as well as the pre-meeting material: this includes the memo calling for the next meeting, and the agenda for the meeting. As an example, you can see the material from the most recent CIR meeting in June 2014. The CIR meets every three months, so there is a LOT of paperwork accumulating around on the site, if you're interested to dig around (they are at meeting number 131 now).

So, although the CIR is industry-funded, as far as industry-funded bodies (or organisations in general) go, they are surprisingly transparent - I mean, even publish the transcripts of the meetings convened so you can see exactly what everyone said, down to the "okays" and "heys". So while they are industry funded, I still find their methods the most reliable source of safety assessments, because 1) they use the available science, so everything is grounded in fact, 2) the panel consists of people who actually are qualified to make an assessment (that's a problem with stuff you read on the internetz), and 3) everything is published publicly. I don't know which other body is quite as transparent, and to me, regardless of the source of funding, if the methods and processes used by that organization stand up to scrutiny, then I would still accept their conclusions. If their processes and methodologies are rigorous, then yes, the results still hold, regardless of where the funding comes from.


A summary of the decision-making processes of the CIR and the EWG. Between the two, I believe the CIR is much more transparent.
In contrast, let's take an advocacy group, like EWG for example, which some people hold as a reliable source, and see how they make their safety assessments. The EWG rates ingredients as "safe" or "unsafe", but there is no indication of how they ever come to this conclusion. They often make statements like "95% data gap" without explaination or justification, and sometimes even when there is plenty of literature out there. The literature they look at is also often selective and limited - for example, for the data on Methylparaben, they look at a grand total of 15 sources, and most of them aren't even scientific literature! The bulk of them are government rulings on parabens (so summaries of scientific literature, which is fair enough but is what I'd expect a layman to use, not an expert), and then trade and industry sources (like trade journals and so on) and then a few scientific papers that they cite. This isn't really a very thorough review by any means. This is is a fair enough way of doing research if you're a layman like me looking for a quick guide to what is out there, but not if you claim to be an expert assessing the research. If you claim to be an expert, and if you are going to act as an advisory organisation to consumers telling them what they should and should not be concerned about, then in addition to summaries, you should bother to exhaustively look at all the other 100+ scientific papers out there, otherwise your views aren't as credible.


The EWG's entry on Methylparaben, which makes the inaccurate claim that there is "strong evidence" of Methylparaben being a "human endorcine disruptor"
Furthermore, the data is often misinterpreted. For example, in the entry for Methylparaben, the EWG claims that there is "strong evidence" that it is a "human endocrine disruptor". They cite as their proof for this an article called "European Commission on Endocrine Disruption" with the year 2007. That makes you think that somehow, in 2007, the European Commission must have said parabens were human endocrine diruptors.

But this is not the case when you actually look at the documents! While the European Commission certainly is a reliable source, it does not actually make the claim that Methylparaben is an endocrine disruptor, or that it is unsafe. In fact, if you look at all the documents released by the Commission (and there are 5 documents, from 1999, 2001, 2004, 2007, and 2011), you won't even find parabens mentioned in the document! Instead, the relevant part of the latest 2011 document says this:

"Although substances with endocrine disrupting effects are currently not restricted under Regulation (EC) 1223/2009 on cosmetic products, Article 15(4) calls upon the Commission to review this Regulation with regard to substances with endocrine-disrupting properties, when EU, or internationally, agreed criteria for identifying substances with endocrine-disrupting properties are available, or at the latest by 11 January 2015. In 2010, the Commission appointed a panel of experts to report on the current status and future prospects on alternative (non-animal) methods for cosmetic testing, and to provide realistic estimates of the time required for the development of alternative methods where not already existing. Among the evaluated tests, alternative methods aiming to detect endocrine active compounds have been considered as part of reproductive toxicity testing."

Below is the screenshot from the actual document itself:


Contrary to the claims made in EWG, the European Commission document doesn't even mention parabens by name, let alone claim that they are endocrine disruptors.
I'm not going to pretend I understand all of that, but it is clear that nothing in here names parabens or any paraben as endocrine disrupting. Essentially, this is a document setting the legal framework for how to go about testing for endocrine disrupting effects using alternatives to animal testing, if such methods become available. (Let's not get started on animal testing here, this blogpost is long enough as it is.) So the documents put out by the European Commission are all legal or policy documents, not scientific ones, yet the EWG takes these legal documents and use them as the scientific basis for saying that Methylparaben is an endocrine disruptor. That just doesn't make sense. Imagine a legal contract drawn up between a buyer and seller of a house, stating how to determine the price of the house, and the time of the buy/sell transaction. Now, imagine taking that legal contract, and using it as a basis for saying that the house has lots of unsafe mould and fungi growing in it and is unsuitable for people to live in. That's roughly the sort of comparison we're drawing here.

Which brings me to another point. Who reads these documents anyway, and makes such less-than-accurate claims based on these documents? We don't know. There is also no indication of who assessed the data, and there is no public record of how the decision was made - no minutes of meeting, no transcripts, no agendas, nothing. In fact, sites like EWG often class ingredients as unsafe when the data is actually to the contrary, and cosmetic scientists (like Colin, whose blog I read), are sometimes puzzled when they come across such sites - you can see his take on one of EWG's entries here. Perhaps it's due to the fact that EWG is an advocacy group that is founded by two personal injury lawyers, so they are more like a lobbying group than a non-profit charity. This could explain some of their behaviour. But regardless of whether the group originated from lawyers or not, until the EWG and all similar groups can cite relevant sources and evaluate them properly, share who their decision-making panel is (is it other lawyers? scientists? who?), and put up all their meeting minutes and transcripts online the way the CIR does, I'm not really convinced by them. The processes they go through are one big black box, and they don't give much information on how their decisions are made. Their description of their methodology on their website is really quite general - it outlines broadly the general rubric for assigning a 0 or 100 or other value, and cites some general sources, but when you look at the actual science available, and the ingredients ratings that specific ingredients get, there can often still some discrepancy. The best part is, among such advocacy sites, they're probably one of the more rigorous ones already - at least they bother to attempt to look at the science! There are entire sites dedicated to the same mission, but sans facts. These sites seem to be more scaremongering than actually informing consumers to me.

C. Thanks! So far you've talked only about USA-stuff, what about other parts of the world? Are parabens deemed safe too? I heard that they are banned overseas.

Sometimes you read online on scaremongering sites that parabens are only allowed in the US because the US government sucks and is negligent, but more responsible governments overseas ban the use of parabens. I'm afraid that's not true.

Outside of the USA (where lobbying from lawyers doesn't seem to have spread to cosmetics yet), the European Commission has also looked at the safety of parabens and found them to be safe. In Europe, parabens can be used in cosmetic products at concentrations of 0.4% for any individual paraben and 0.8% for total paraben concentrations (i.e. a mix of parabens). And the Japanese regulatory authorities also allow parabens (you won't find parabens mentioned in the document - basically the Japanese system works by exclusion, so if it's not listed there, it's fine for use, but if it is, there could be restrictions on its use). Canada's rulings follow that of the US. In fact, parabens are allowed for use pretty much in every place that bothers to regulate cosmetics - you can see this overview of cosmetic regulations worldwide (it deals with issues beyond ingredients, including labelling, definitions of cosmetics in different regions, and so on).

And all three major jurisdisctions that make their own decisions - USA, Europe, and Japan - allow parabens to be used in cosmetics in small quantities as a preservative. As a matter of fact, all three governing bodies also allow parabens for use in food, too, so it seems a little unfair to single out parabens in cosmetics for selective bashing, although that is what we see today.

2. If parabens are safe, why are they so controversial? Where does the hype come from?

So, if parabens are safe, why all the hype? Most people who dislike parabens believe that parabens cause breast cancer. This view is actually derived from a bit of misinformation with lots of fearmongering thrown in. The source comes from a 2004 study where scientists took breast tissue from 20 women, and found that there were parabens in the breast tissue.

This study was not conclusive by any means because:
1) The researchers didn't look at paraben levels in breast tissue that wasn't cancerous. After all, water is in cancerous breast tissue too, but it doesn't cause breast cancer! So without comparing against cancer-less tissue, we can't draw any conclusions, and
2) The authors are not able to prove that parabens actually caused the cancer (correlation is not the same as causation, after all)

But people twist the results and selectively misinterpret them, and the vast majority of "omgz parabens cause cancer" type of online views are written as though the authors have proven that parabens cause cancer. It is a deliberate misinterpretation of the results, and a lot of misdirected hype. I say "deliberate misinterpretation" because if we actually look at what the original study's authors conclude from their own results, they don't even claim that parabens cause breast cancer, only that there are parabens in breast tissue and this needs further study: "These studies demonstrate that parabens can be found intact in the human breast and this should open the way technically for more detailed information to be obtained on body burdens of parabens and in particular whether body burdens are different in cancer from those in normal tissues." (In other words, scientist-speak for "We've noticed that this exists, but we don't know why or how and we can't jump to conclusions about it. So it needs more study.") This is very different from what you read on those Internetz sites which act as though parabens have been proven to cause cancer, because people misinterpreted and sensationalize the data, and often, lobbying groups like EWG and so on are less than honest in how they represent scientific studies and data. In fact, this very same study is addressed by the FDA on their website, and I'm quoting from the relevant bit of the article: "A study published in 2004 (Darbre, in the Journal of Applied Toxicology) detected parabens in breast tumors. The study also discussed this information in the context of the weak estrogen-like properties of parabens and the influence of estrogen on breast cancer. However, the study left several questions unanswered. For example, the study did not show that parabens cause cancer, or that they are harmful in any way, and the study did not look at possible paraben levels in normal tissue. FDA is aware that estrogenic activity in the body is associated with certain forms of breast cancer. Although parabens can act similarly to estrogen, they have been shown to have much less estrogenic activity than the body’s naturally occurring estrogen...Further, parabens are used at very low levels in cosmetics. In a review of the estrogenic activity of parabens, (Golden et al., in Critical Reviews in Toxicology, 2005) the author concluded that based on maximum daily exposure estimates, it was implausible that parabens could increase the risk associated with exposure to estrogenic chemicals." So as you can see, both the FDA and the authors of the original study are not able to make any links between paraben use and breast cancer.


A table in the 2004 research paper, showing average concentration of parabens found in the breast tissue, as well as confidence level. For concentrations, they are using the measure ng/g, i.e. number of nanograms of parabens per gram of breast tissue. 1 ng/g means 1 gram of parabens occurs every 1,000,000,000 grams (or 1,000,000 kg, or 1,000 metric tons) of breast tissue. (So even the highest paraben recordings occur at very low rates.) (Source: J Appl Toxicol. 2004 Jan-Feb;24(1):5-13. Concentrations of parabens in human breast tumours. Darbre PD et al.)
As a matter of fact, the vast majority of scientific studies available reaffirm the safety of parabens. You can get a neatly summarized overview of the other studies done in the CIR reviews on parabens. I use the CIR source because it lists virtually every study on parabens done to date, so it is very useful as an overview (if you're suspicious on whether they are leaving out studies, you can go to Pubmed (my favourite online repository of biomedicine and health literature), and search for keywords like "paraben" and "topical" and "safety" - you'll find that all the results that you get that are relevant are cited by the CIR). When I did a quick count of the number of citations the CIR report had, it had over 130 citations, from various sources including non-profits like WHO, academic journals (the most common source by far), other government rulings, and CIR's own past studies. Some are duplicate citations (because different annexes may cite the same source), but you get the vast amount of data they are looking at. So as you can see, the vast majority of scientific data shows that parabens are not harmful as they are used today in our cosmetics, and all the major governing bodies have looked at this data and have concluded that parabens as used today are safe. In fact, even the American Cancer Society has also stated, based on the scientific literature available, that "studies have not shown any direct link between parabens and any health problems, including breast cancer. There are also many other compounds in the environment that mimic naturally produced estrogen." Yet, there is so much misinformation and fearmongering going on just based on one single study done 10 years ago that doesn't even show any link between parabens and breast cancer (or any other form of cancer, for that matter). So this is exactly what I meant when I said that the established safety data on parabens doesn't warrant the current hoopla about them - it seems to me like the hysteria and fearmongering just got out of hand, especially when some sources don't seem to fact-check against actual scientific data.

Obviously, fearmongering is a trade as old as time. (Image Source)

In any case like I mentioned, parabens are found everywhere - not just blueberries and grapes, but also wastewater, rivers, soil and house dust. So even if parabens were a concern, we shouldn't be focusing only on cosmetics and skincare. We should really be looking at our environment in totality, including food (because we ingest it), as well as the general surroundings that we are exposed to on a continual basis, rather than a jar of cream that contains 30ml of product (of which parabens are less than 1%, or 0.3ml) that a consumer uses up in, maybe, 6 months, with daily usage.

So why are we so focused on parabens specifically and skincare and cosmetics? This is probably where I'd like to look at all the lobbying sites and organisations, where the focus is exclusively on cosmetics. Because such sites have fearmongering tendencies, and behave like lobbying groups (in other words, they act with an intent to influence and sway the views of the general public, and spread their agenda), whatever they focus on, fairly or unfairly, becomes whatever people hear and read about. If these sites or such groups had focused on say, parabens in wastewater, that is exactly what we would be worrying about now, and noone would focus on cosmetics. As luck would have it, somehow the focus is on cosmetics and skincare despite the comparatively minuscule amounts of parabens we are exposed to through such channels (I'd wager money that the reason for such a focus is probably more a lawyer's reason than a scientist's reason), so this is what the hype is about.

3. If there is so much hype about parabens being bad, why are they still commonly used?

Now that we have looked at paraben safety, we can answer your other question - why are parabens in our products? The reason why parabens are sill in our cosmetics is because they are usually the best choice for preservatives out there, assuming marketing gimmicks (like being able to promote your product as "paraben-free") are not factored in. This means they are 1) effective, 2) safe as compared to other options, i.e. paraben alternatives.

Often, paraben alternatives don't work as well. There are paraben alternatives, but generally, they don't do as good a job as parabens. In order to do a good job as a preservative in cosmetics and skincare, an ingredient has to be effective against both bacteria and fungi. Parabens work against both, but most paraben alternatives, which are acids of some sort, including benzoic acid, potassium sorbate, sodium benzoate and so on, work against fungi but not bacteria. Also, other "natural" paraben alternatives, such as thymol, cinnamaldehyde, allyl isothiocyanate, citric acid, ascorbic acid and rosemary extract, only work in lab conditions (like a petri dish), but when actually tried out in real life (in this case into food), have much lower effectiveness.

Some paraben alternatives are also actually less safe than parabens. For example, some forms of paraben alternatives include formaldehyde, quaternium-15, imidazolidinyl urea, diazolidinyl urea and dimethyloldimethyl hydantoin, but these can cause allergic reactions and some pose more serious health implications. This applies to even "natural" sounding alternatives, like grape seed extract, which can interfere with some medications.

So with this in mind, it seems to me that, ironically, the very people who are pushing for parabens to be removed from our cosmetic and skincare products, supposedly in the name of safety, are actually making our products less safe. In effect, they want to remove a perfectly fine ingredient that has been justified by almost all the available scientific data, and replace it with other ingredients that may not be as effective or safe, or have other complications.

4. And now, a bonus answer to a question you didn't ask: What happens to parabens when you apply them to your body, anyway?

Noone ever asked me this question, but I thought it's worth a mention because, well, this is at the heart of the debate. After all, all the scaremongering and hype about parabens in cosmetics is based on the assumption that parabens, when applied to skin, is somehow absorbed by the skin and enters the body, where it mimics estrogen (exhibits estrogenic behaviour), and thus causes cancer by playing haywire with your body systems. But what actually happens when we apply parabens to our bodies?

Well first, parabens have to be applied to our skin. Then, our skin has to absorb them and they have to go into our bodies. But before they do, enzymes in the skin rapidly metabolize parabens to PHBA, the primary metabolite, reducing the dose that reaches the blood stream. So even before your body absorbs the parabens you apply, some of it is already broken down. (If you're curious to know, how much is absorbed and how much is not, then the longer the length of the ester side chain (i.e. the "bigger" the molecule) the less of it gets absorbed by our skin. So this means that butylparaben penetrates the least, followed by propylparaben, then ethylparaben, and lastly methylparaben).

After that, the remaining parabens are metabolized by keratinocyte carboxylesterases and the conjugated metabolites are excreted in urine and bile. So, parabens can indeed get absorbed into the body. That part of the hype is true. But, they are degraded on the skin before absorption, so not all of it enters the body, and when it does, body actually breaks them down into other substances that are then gotten rid of when you pee (in your urine) or when your liver does its work (in your bile). So yes, your body is perfectly capable of breaking down parabens it is exposed to. If you eat the parabens (rather than applying them), then these also are metabolized by esterases within the intestine and liver, or in human-speak, your liver and intestines have enzymes that break them down. So whether by application or by ingestion, your body can handle the parabens.

But in any case, parabens are 1,000–1,000,000 times weaker than natural estrogenic compounds, so even if your body didn't break them down the way they did, you'd probably have to use very, very high amounts of parabens in order to get them to actually change the way your body functions. In fact, natural estrogens (or those taken as hormone replacement) are much more likely to play a role in breast cancer development. But since your body has ways of breaking it down, it's not really a concern.

In fact, the only real harm that parabens can cause is to people who have an allergic reaction to them. Parabens, as is the case for many preservatives, can cause allergies, in the form of an eczema-like rash, for a small group of people. But even then, in order to trigger the allergy, the concentration of parabens needs to be from 0.5% to 3.5%. Given that cosmetics and skincare use them at rates below 1%, even for people with such allergies, the large bulk of paraben-containing products would be unlikely to trigger such allergies. For what it's worth though, most common sensitizers trigger allergies at much lower rates, so comparatively, parabens are considered to be non-irritating and suitable for sensitive skin.

Oh, and as a side bonus, it's not just our bodies that can breakdown parabens - this also applies to our environment in general. The US CDC notes that parabens do not persist in the environment, and they are degraded by photolysis in the air and biodegraded in water, so there you go - they are broken down in the presence of air and water.

TL;DR - Can You Just Summarize it for Me?

So to sum up - my conclusion is based on several key points I've touched on over the 4 headings:

1. The bulk of scientific data shows that parabens are safe, and they are determined to be safe for us in almost all jurisdictions
2. The scientific literature that fuelled the anti-paraben movement can't prove causation, and in any case the authors themselves say that they can't draw a link and further study is needed
3. Your body breaks down parabens applied topically through urine and bile
4. Parabens are used in tiny concentrations at less than 1% in cosmetics and skincare
5. Paraben alternatives are not necessarily safer, or more effective
6. Parabens are broken down naturally in our environment

I know this is not the English"parabens" but "parabéns", the Portuguese word for "congratulations", but I thought the meaning was quite amusing in English anyway. (Image source)

So given all this, my conclusion is that there is no cause for worry, despite all the fearmongering on the Internet, unless you happen to be one of those people that develops a rash to parabens. And even then, chances are, the bulk of paraben-containing products would still be fine for you. I'm sure tons of people will disagree with me (it's likely when the hype is very high and lots of people have bought into that point of view), and it's certainly their choice to come to their own conclusion and hold their views. But for me, I always strongly prefer being able to base my views on scientific evidence, rather than basing it on fearmongering and hype, or worse still, twisting the science to fit my viewpoint.

So that's it for my monologue! Congratulations if you've managed to read this far, because it means you have the patience of a saint, and the concentration of an air traffic controller. I hope my little summary of the scientific literature out there has helped you!

Annex: References

I've included some references and info on parabens and their safety, because I know that a google search often throws up all the fearmongering sites, making it hard to find the reliable sources of information. Some of these sites are already mentioned in my article, some are not, but all of them are useful information:

1. US CDC Biomonitoring Summary on Parabens: http://www.cdc.gov/biomonitoring/Parabens_BiomonitoringSummary.html
2. US CDC paraben fact sheet: http://www.cdc.gov/biomonitoring/pdf/Parabens_FactSheet.pdf
3. Info on the FDA's website on parabens as found in cosmetics: http://www.fda.gov/cosmetics/productandingredientsafety/selectedcosmeticingredients/ucm128042.htm
4. News summary of CIR's stand on parabens: http://prnewswire.com/news-releases/cosmetic-ingredient-review-cir-expert-panel-reaffirms-the-safety-of-parabens-used-in-cosmetics-and-personal-care-products-141750543.html
5. Full summary of the decision made by the CIR on parabens. It is referred to in the press release above, and is super long but quite useful as it goes into detail on what exactly are parabens and contains a summary of the scientific literature on parabens to date. If you have some chemistry background you will also appreciate their in-depth look at the properties of parabens: http://www.cir-safety.org/sites/default/files/paraben_build.pdf
6. A summary of the European Commission's stance on parabens: http://ec.europa.eu/health/scientific_committees/consumer_safety/docs/sccs_o_041.pdf
7. Japanese regulation on cosmetic ingredients: http://www.mhlw.go.jp/file/06-Seisakujouhou-11120000-Iyakushokuhinkyoku/0000032704.pdf
8. Canadian regulation on cosmetic ingredients, including parabens: http://www.cctfa.ca/site/eblasts/DSF_1110/HC_Letter_181010.pdf
9. An overview of cosmetic regulations worldwide (from the ChemCon Asia 2013 conference):
http://www.lawbc.com/share/chemcon2013/Conference%20Handouts/11%20September%202013/Session%208-4.pdf
10. The Health Controversies of Parabens, by Mark G. Kirchhof, MD, PhD, Gillian C. de Gannes, MD, MSc, FRCPC. Published in Skin Therapy Letter. 2013;18(2): http://www.medscape.com/viewarticle/780590_1
11. Parabens, Carcinogens and Certified Organic Ingredients, by Rebecca James Gadberry, January 2006 issue of Skin Inc. magazine: http://www.skininc.com/skinscience/ingredients/21411264.html
12. American Cancer Association article Antiperspirants and Breast Cancer Risk (also touches on other ingredients in antipersperants, not just parabens: http://www.cancer.org/cancer/cancercauses/othercarcinogens/athome/antiperspirants-and-breast-cancer-risk
13. Paula's Choice article on parabens, useful for links to other sources: http://www.paulaschoice.com/expert-advice/myths/_/parabens-are-they-really-a-problem
14. Personal Care Council Paraben Information: http://www.cosmeticsinfo.org/HBI/9
15. Parabens: A Review of Epidemiology, Structure, Allergenicity, and Hormonal Properties; by Allison L. Cashman, Erin M. Warshaw; Published in Dermatitis. 2005;16(2):57-66.: http://www.medscape.com/viewarticle/508430_2
16. Futurederm blog post - well, this is a blogpost so normally I wouldn't consider it a reliable source, but it is grounded in science, and has links to even more useful referencess: http://www.futurederm.com/2012/11/27/are-paraben-alternatives-actually-better/
17. Comment by Gaëlla Azzi, R&D Biotechnologist at Europelab Inc. on the link between parabens and breast cancer: http://europecosmetics.ca/?p=85