Have you heard that 60 to even 90% of cosmetic ingredients are able to penetrate your skin into your body? Upon reading about this concern from other beauty brands and from some of our followers, I just wanted to write a quick blog post to take you through this topic. In this post, I’ll take you through the biology of your skin, how it protects you from the environment around you, how and which substances can penetrate through the skin and why, regulations in cosmetics, why the above percentages aren’t based in reality, important things to know about your cosmetics, and lots more. Enjoy!
Skin, what’s it really good for?
At the end of the day, the skin on your body provides you with a relatively tough, sac of sorts to surround and protect your delicate insides from the harsh environment around you. Protection is its main function, and it does this in a number of different ways. For example, the natural pH of your skin is roughly 5.5; this, as well as sebum, helps to control the number and growth of the bacteria that flourish here. Melanin, a chemical secreted from your skin, helps to protect your skin from UV rays. Aside from this ‘chemical’ protection, the skin itself acts as a physical barrier. The layers of hard, keratinized cells prevent things from easily penetrating down into your body. The skin also has a number of immune cells, like Langerhans’ cells for example, which are present in the top layers of your skin, at the epidermis. The skin helps to regulate temperature, has metabolic processes that are important for our overall health, for example creating Vitamin D from sunlight, helps to excrete waste from the body through sweat, and so much more.
The biology of your skin tells you a lot about how you should be treating it, including what types of cosmetics you should be using and why they may work. It also tells you a lot about what may penetrate into your skin and why, but more on that later. Here’s a quick diagram that we made to give you a good overview of the basic biology of your skin.
I know the above infographic is a wee bit sciency. To make things easier to understand, we also made this quick video to take you through all of the information above!
If you’d like even more detail about the biology of your skin, you can listen to the below interview with Dr. Katerina Steventon from our podcast. In this episode, we took a deep dive into the biology of your skin.
Absorbance into the skin
With all of that in mind, when you take a look at the structure of your skin, you can get a good idea of how and why certain ingredients may or may not penetrate into your body.
The top layer of your epidermis is a structure like bricks and mortar. Your skin cells are tightly packed into the fatty intercellular mortar.
For chemicals (note, everything's a chemical :) to pass through the stratum corneum (the top layer of your skin), they either have to pass through the skin cells or around them (i.e. through the fatty mortar). To give you some context, below are the size of a few relevant items.
- Stratum Corneum ‘Hydrophilic’ Paths: 0.4nm
Note, ‘hydrophilic’ (e.g. water soluble) paths would be MUCH smaller.
- Cell Membrane: 6-10nm
- Stratum Corneum Lipid Bilayer:13nm
- Stratum Corneum Intercorneocyte space: 20-75nm
- Stratum Corneum Thickness: 10,000-40,000nm
- Diameter of your Hair: 80,000nm
As you may be able to see from these sizes, water-soluble substances need to be VERY small to make it through the stratum corneum. Fat-soluble chemicals can travel through the lipid bilayers when small… but comparatively speaking, they still have huge distances to travel to make it to just the deeper layers of your epidermis, let alone to your dermis or to your bloodstream. Because of the complexity of your skin and all the different layers, for substances to potentially make it down to the deeper layers of your skin, they’d have to be smaller than 1000 daltons if they’re in an amphiphilic base (e.g. an emulsion that contains both hydrophilic (water) and hydrophobic (oil) phases as well as the amphiphilic substance (emulsifier), e.g. lotion). Even still, they’ve got a comparatively ginormous distance to travel after that to make it to just the dermis. In addition, the substances would be challenged by the changes in for example pH, polarity, solubility, your immune cells, etc. as they move to the deeper layers of your skin. As a result, most cosmetic products have extremely limited penetration and sit mostly on the surface of the skin.
Cosmetic products may…
- Sit on the top of the skin and potentially penetrate a wee bit to the stratum corneum (the outer layer of your skin). This provides moisture to your skin and helps to reduce water loss, helping to improve the appearance of your skin overall. With color cosmetics, the products will temporarily stain the top layers of your skin.
- Penetrate past the top layer of your skin to the middle part of your epidermis (stratum granulosum). For example, humectants can do this. When they do, they will attract water from the environment and deeper layers of the skin to give you more supple looking skin. As a result, active ingredients are often paired with humectants (e.g. glycerin, butylene glycol) to pull them to the stratum granulosum.
- Penetrate to the deeper layers of your epidermis (stratum basale). For example, certain cosmeceutical substances like peptides, which may stimulate skin changes, for example with collagen synthesis (note, if they’re able to have this type of deep penetration and skin effects, the products will often be regulated as a drug by law in North America, unless they don’t claim the effects on the label…). These changes are transient, i.e. once you stop using the product, the changes will go away quickly. To achieve this level of penetration, the active ingredients are often put in an emulsion base combined with a humectant and/or some sort of delivery agent.
Very few cosmetic ingredients will penetrate to the dermis, and even when they do, they’ll often be acted on by macrophages to remove them before they enter the bloodstream. This is different than pharmaceuticals (e.g. steroids) or injected cosmetic substances (e.g. sodium hyaluronate)... but this discussion is about cosmetics. If a cosmetic product has that sort of penetration, it must be regulated as a drug here in North America, which have way more regulatory and safety requirements for this reason.
Note, cosmetic ingredients are regulated by their size, as well as a lot of other things. Ingredients that are small enough to penetrate into your bloodstream are generally not allowed in cosmetic products.
Note, we’re talking about skin that’s intact. Cosmetic products aren’t generally meant for broken skin (that’s where the cosmetics regulated as drugs come in). Obviously, when cosmetic products are applied to broken skin, a lot more of its ingredients have the opportunity to penetrate.
There’s A LOT going on here to get the full gist of the skin and absorption of ingredients in a single blog post. Considering that certain cosmetic ingredients are frequently found in our urine or blood, clearly, some ingredients used in cosmetic products may be able to penetrate… but 60-90%, I think not. If ingredients are able to penetrate, it will be in very very very small proportions. Because of all of the complexity as noted above, there won’t be a set percentage that anyone will be able to truthfully give you about the ingredients in your cosmetics and their absorption into the body. I think we should be thinking about the ingredients in our cosmetic products, but for people working in the cosmetic industry, we should also be making accurate claims and trying to maybe stray away from fear mongering, especially when it’s not based on good evidence and only on pseudoscience… That’s my two cents and that’s a wrap. Questions, queries, conundrums or concerns? Give us a shout on social media or reach out to us at firstname.lastname@example.org. Thanks for reading!
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