Mineral Oil Myths Explained: Cancer, Safety, and Skincare Benefits

Monday, August 12, 2019

It's been awhile as life has gotten busy! But I'm back with more skincare geekery - this time on mineral oil! I've wanted to write this post for awhile, because over my years being an amateur skincare nerd, I've noticed lots of fearmongering with respect to mineral oil. Some people believe that 1) mineral oil is bad for you because it prevents your skin from breathing, 2) mineral oil causes cancer, or that 3) you shouldn't use it because it is derived from petrochemicals. I'll be taking a look at these three myths in this post!

First though, a little bit of a primer into mineral oil itself.

What is mineral oil?
Mineral oil is a liquid mixture of hydrocarbons (i.e. molecules comprised only of carbon and hydrogen atoms) obtained from petroleum, and consists of saturated hydrocarbons having carbon numbers predominantly in the range of C15 through C50. As seen in the bottles of baby oil, it is easily recognizable as an oily transparent liquid. It's manufactured by the distillation of petroleum, and then followed by refining of residual fractions to meet the standards for cosmetic grade mineral oil.

Incidentally, although I'm talking specifically about mineral oil in this blogpost (because it's the ingredient that does seem to have a lot of myths surrounding it), some of the information also applies to other similarities ingredients, such as petrolatum, and some other hydrocarbon oils and waxes as seen in the table below.

Some other ingredients with similar properties to mineral oil (Source)

The physical properties and functions of these ingredients are pretty much the same as used in cosmetics and skincare, but the difference arises primarily from the length of the carbon chain. In short, all the ingredients are made up of variously arranged chains of carbon and hydrogen atoms, but have different lengths of the carbon chain, which in turn affects the size / length of the molecule, and other physical properties, as longer carbon chains tend to give rise to larger molecules, which in turn tend to be more solid at room temperature. Obviously the ingredients above are not identical, but they would have pretty similar functions in skincare.

What does mineral oil do in cosmetics and skincare?

As you might expect with an oil, it forms a layer on skin and basically functions as an occlusive moisturizer, i.e. it keeps skin moisturized by forming a barrier between the skin and the skin's surroundings. The barrier it forms helps the skin to retain moisture, because a large part of the cause of dry skin is transepidermal water loss (TEWL), which is a term you see in the scientific literature that simply means evaporation of water from the skin to the skin's environment. This rate of water loss from the skin can be worse if your skin's own natural barrier is already damaged, e.g. in people with skin conditions, or if you live in very harsh and dry environments. So for such people, applying a lotion or cream that forms a barrier helps to reduce TEWL, and thus keep the skin's moisture levels intact, as the diagram below shows.

Mineral oil forms an occlusive layer on skin. This is NOT a bad thing, but a good thing, as it prevents TEWL. (Source. Interesting tidbit: this diagram is from a published paper entitled "The Infant Skin Barrier: Can We Preserve, Protect, and Enhance the Barrier?")

Mineral oil has been used this way for ages, and there is a history of "long and uneventful human use of white mineral oils in drug and non-drug topically applied products". It's a simple ingredient with not much ado about it, because it has been used without incident in skincare and cosmetics for so long.

In fact, because mineral oil is so well established as a moisturizer, it is often used as a benchmark when trying to establish how occlusive/moisturizing other compounds are. This includes compounds like extra virgin coconut oil (the study concludes that “coconut oil is as effective and safe as mineral oil when used as a moisturizer.”), and vegetable oils (the conclusion of the study: “These data indicate that there is no statistical difference between the paraffin oil and vegetable oils in terms of skin penetration and skin occlusion.”). It was even used as a baseline for things like kukui nut oil for treatment of psoriasis (again, no difference between the two was found), and topical fish oil for psoriasis (here there was a difference - fish oil was found to help psoriasis better, but was also more likely to cause allergic reactions).

Mineral oil is well established as a moisturizer, and is often used as a benchmark when assessing how moisturizing other compounds are, and this science conference poster is a good example of this benchmark at work. (Source)

So to sum up, it's a pretty well-established occlusive and for that reason is a pretty good moisturizer. Most moisturizers (and other skincare products) on the market would have combination of water, humectants (such as glycerin) and emollients and occlusives as key ingredients, and mineral oil is a pretty effective occlusive, which is why you see it popping up in ingredients lists.

Myth 1: Mineral oil prevents skin from breathing, and it's better to use other "natural" oils instead.

Some sites/blogs like to make claims like how mineral oil is equivalent to suffocating your skin in plastic wrap and will clog pores. The underlying assumption behind this assertion is that such sources assume that applying a barrier layer like mineral oil will prevent the skin from absorbing water and thus dry the skin out, which might just be true in theory if your skin was drier than the environment (which is generally not the case). But in real life, people get dry skins because whatever water is in their skin is being lost to the environment, and mineral oil doesn't actually stop other ingredients from reaching your skin.

If you're not comfortable with using mineral oil, then you're certainly welcome to use another oil, but it would basically work the same way mineral oil does, i.e. to form an occlusive layer on skin. This is also the case with "natural" oils such as coconut oil, and other vegetable and botanical oils. In fact, extra virgin coconut oil and vegetable oils are as occlusive as mineral oil is (in other words, they have the same barrier-forming properties). So they can certainly serve as a replacement (especially if you are picky about skinfeel, because mineral oil does feel heavier than some lighter oils), but they aren't particularly better or worse in terms of functioning as an occlusive.

Final note on this is that most oils applied to skin also form this occlusive barrier - it's just how oils in general work as moisturizers, but for some reason other oils don't get as much negative press as mineral oil does. Different oils have different barrier forming effects because some are more lipophilic than others, and yes you can feel the difference on your skin, but generally most oils will exhibit this to some degree. So I don't really see much of a point behind singling out mineral oil as a bad guy for being occlusive when pretty much any other oil does that.

With respect to mineral oil and acne - does mineral oil cause acne? There isn't anything to suggest that it does (indeed mineral oil is reputed to be particularly non-reactive), but, if your skin doesn't like it, and you're concerned that it might be making your acne worse, then of course, you can seek products without it.

Myth 2: Mineral oil is derived from petrochemicals, so that mean it's not safe to use on my face

This rationale here is "mineral oil is derived from petrochemicals. Gasoline and industrial lubricants are also petrochemicals, which could be toxic and which I don't want on my face. Therefore, I don't want mineral oil on my face". It's true that mineral oil would indeed be a concern if it did contain gasoline and other petrochemicals that shouldn't be used in skincare products, but the manufacturing process for mineral oil that have been refined to meet the various standards for mineral oil (USP for US markets and BP for British standards) would exclude most of the harmful petrochemicals that could otherwise be harmful to our skin (and general health).

Generally, a lot of the concern about mineral oil being toxic because of petrochemicals has to do with impurities in the mineral oil, and not the oil itself. Unfortunately the term "mineral oil" is kind of vague, and could refer to different grades of mineral oil, or even industrial oils, and this seems to have been a lot of the source of such bad science. In the journal In Cosmetics, the author, and this see notes that "It is imperative to recognize that the degree of refinement of mineral oil and petrolatum is the key to safe and successful cosmetic formulations. Simply using the terms "mineral oil" or “petrolatum” or “petroleum jelly” is not sufficient. Even the CAS (Chemical Abstract Services) registry numbers for these materials do not fully distinguish quality or refinement. If the term mineral oil is not properly defined, it can refer to the oils used in industrial and automotive lubricants. Likewise, unrefined petrolatum can also be used in industrial applications. Some published reports have not clearly distinguished between refined grades of mineral oils and actually refer to lesser refined mineral oils in the same context as the fully refined grades that are used in cosmetic and pharmaceutical applications. This is a misrepresentation that has resulted in confusion in the industry over time". So a lot of the bad science out there basically confuses cosmetic grade mineral oil with other mineral oils for industrial use that indeed shouldn't be used for topical applications.

Assuming your product is using the right grade of mineral oil for cosmetic applications (which would be the case for most brands and certainly the huge brand names which would be subject to greater regulatory scrutiny), then this isn't a huge concern. This is because the manufacturing process for mineral oil "is designed to exclude substances with carcinogenic potential like polycyclic hydrocarbons (PAH) and to minimize the presence of aromatic compounds, referred to as ‘MOAH’ (mineral oil aromatic hydrocarbons), which are inevitably present in the crude mineral oil starting material" - in other words, mineral oil that has not been refined properly to the cosmetic standards is an issue, but properly refined mineral oil should not contain any contaminants.

Myth 3: Mineral oil causes cancer

This is a pretty common one (along with baby powder causing cancer, which I've dealt with in another blogpost), but mineral oil has been assessed as safe by the US CIR (Cosmetic Ingredients Review) and the European Comission since the 1970s, and both have long histories of use with very little side effects.

When I browsed through the papers availble on Pubmed, I couldn’t find any evidence of health risks arising from mineral oil when used in skincare. There were a couple of studies showing some grades of petroleum oils (including oils heavier than mineral oil, or oils with impurities) can cause skin growths on mice skin with prolonged application, but it seemed to me that 1) such effects are only seen with heavier grade mineral oils (in other words, not the kind used in cosmetics or food), 2) the occurrence of skin effects in mice is not correlated to how carcinogenic the oil is to humans (implication being that even if something is harmless to humans, mice skin might react to it and vice versa, thus making it hard to extrapolate from mice to humans), and 3) fundamentally, these studies only show such effects in mice, and not in humans (because mice and humans are different, as per my previous point). In humans, mineral oil only seems to be a problem if you gargled with mineral oil for a prolonged period of time (and I'm guessing this isn't cosmetic grade mineral oil he was gargling with), or if you inhale it, but that was about all. So no, nothing about mineral oil causing cancer, or drying your skin out, or anything like that. Overall, the reviews on mineral oil safety I came across concluded that mineral oil used topically was safe.

In fact, it's interesting to note that mineral oil, as applied topically (as is the case in skincare and cosmetic products), actually remains on the surface of the skin where it is applied, and is not absorbed into our bodies, so it is highly unlikely to cause cancer, which would require the product to be "reach the systemic circulation via the intercellular or intracellular route or through absorption via hair follicles or sweat glands". But as this review of mineral oil (and the other hydrocarbon oils and waxes), the penetration does not occur, and "the available experimental data on mineral oil and wax type substances consistently indicate that the substances remained in the stratum corneum and only negligible fractions, if any, reached deeper skin layers or systemic", and that this is in line with previous positions that "hydrocarbons with carbon chain lengths greater than C20 to not become systemically available via the dermal route of exposure". In other words, once the molecule exceeds a certain size, it is too large to be absorbed systemically, so it is unlikely to thus cause cancer. And since mineral oil has a chain length of C15 to C50, it would not be likely to be absorbed and cause cancer. For other hydrocarbon oils and waxes with larger molecules (almost all of them), this risk is even more unlikely.

So in short - as far as topical application goes, mineral oil as used in cosmetics and skincare products is pretty safe, assuming your product is indeed using cosmetic grade mineral oil (and not some bootleg industrial stuff). Don't gargle with it, and don't inhale it, and you should be good.

So, if a product has mineral oil, what does it mean?

If a product has a lot of mineral oil in it, then you can probably expect it to be likely to be occlusive and probably have some barrier-forming properties. This can be pretty useful information if you're applying multiple skincare products, as generally you'd want to apply your skincare from least occlusive to most occlusive. For example, if you're applying a very lightweight product with no oils/emollients/occlusives (say, a lightweight lotion with water, glycerin, and maybe some plant extracts), and also applying a heavier cream with mineral oil and a bunch of other emollients, then you'd know to apply the lotion first, before the cream, rather than the other way around. The higher the concentration of mineral oil, the more likely the product will be occlusive, and the more likely you'd want to use it towards the end of your routine.

Secondly, if a product has a lot of mineral oil in it, you can probably expect the product to....well, have the feel and texture of mineral oil. So it might be a bit heavier and more moisturizing if it's a skincare product, or a bit thicker if it's a foundation. Of course, sometimes formulations can have mineral oil and still be very lightweight (for example, a formulation might also include alcohol to thin out the mixture, or replace some of the mineral oil with lighter-feeling silicones), but in general, the higher up the ingredients list mineral oil is (say, if it's in the second or third ingredient), then the more likely the product will have a thicker / heavier / oilier skinfeel. This can also be useful information if you're say, ordering a foundation sight unseen online because there's a great deal and you figure it can't hurt to try (not that I wouldn't know....haha jk, I've totally done that before when sales were too good to pass up!). Having the ingredients list, and being able to make a very rough guess as to the texture of the product can be helpful.

But, it does NOT mean that the product will cause cancer, or be bad for your skin or anything like that. You might or might not like mineral oil because of its texture (which is, I think, partly why silicones are so popular nowadays in formulations, as they give a lighter, more pleasant skinfeel in addition to not getting as much scientifically inaccurate bad press as mineral oil does), but as it is currently used in cosmetics and skincare, mineral oil should be safe to use, and it won't cause cancer.


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