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Do cosmetic ingredients really penetrate skin? Episode 92

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Do cosmetic ingredients penetrate skin?

Chris says…Can you guys talk a little bit about ingredient penetration? Why do some ingredients penetrate skin while others won’t? What mechanisms and conditions are involved?

Let’s start our discussion about the truth of skin penetration by mentioning a few popular misconceptions on the subject.


One of the reasons we wanted to tackle this topic is that there’s so much misinformation out there. I think most consumers of beauty products have seen the fear mongering headlines like the following:

  • Our skin absorbs __X__ number of pounds of cosmetics each year.
  • A “high percentage” of everything we apply to our skin every day penetrates.
  • EVERYTHING that we apply to our skin penetrates into the blood stream.
  • If a chemical is found in human urine, that means the cosmetic it came from is dangerous.
If skin didn’t absorb everything we apply to it, then why does a medication patch delivery work so well?

If these headlines were true we wouldn’t have to eat because we could absorb nutrients just by rubbing food on our skin. That’s obviously not the case, although it’s true that SOME chemicals can penetrate skin.

Now, in a single 30 minute show we can’t do a deep dive into the data for every cosmetic ingredient used in every product but we can explain…

  • How skin penetration works
  • The 4 main factors that control skin penetration
  • And perhaps the most relevant question – is penetration necessarily a bad thing.

How skin penetration works

Let’s do a very quick review of skin biology. Skin has evolved to be a protective mechanism. It is literally a barrier to separate us from the outside world. It’s composed of 3 main layers…

“Epi” is a Greek term is used as a prefix meaning upon or or above so the epi-dermis is the layer that’s upon or above the dermis. This is the part of skin that you directly interact with. It’s important to understand that the outer layer, called the stratum corneum, is dead. The thickness of this layer does vary based on location. It’s very thin on your eyelids, for example, and much thicker on the bottoms of your feet. 
The lower levels of the epidermis are where new skin cells are made. It’s also the layer responsible for making melanin which gives skin its color. 
And as we already said, its responsible for protecting your body.

The next layer, the dermis, is where body hair, sweat and oil come from. It’s also home to nerve endings which are responsible for your sense of touch. There are also blood vessels in the dermis.

The bottom layer of skin is the subcutaneous fat layer which is also called the hypodermis. This layer basically attaches the upper layers of skin to the bone and muscle below. The fat insulates you from temperature variations as well as physical shock, and it contains even more, larger blood vessels.

So, as you can see, an ingredient has quite ways to travel before it can penetrate completely though your skin. Next let’s talk about exactly what determines how well that penetration will work.

We talk about this level of skin using the “brick and mortar” analogy because you can think of the skin cells as tiny bricks stacked up on one another with some sort of mortar or cement in between them. So this is where we start our discussion of skin penetration because to get into the skin the first thing an ingredient has to do is find its way in between those layers of brick and mortar.

Now let’s talk what mechanisms are responsible for this penetration and what conditions control the degree of penetration.

4 Factors that control skin penetration

1. Size/molecular weight
An important factor is the size of the molecule which is tied to its molecular weight. Most molecules are simply too large to slip between those cracks between the “bricks” of the dead skin cells.

There are some surprising exceptions for example in Episode 75 we talked about the discovery of that hyaluronic acid can make its way through the skin. But by and large the smaller molecules will penetrate better. The rule of thumb is that anything smaller than 500 Daltons can penetrate skin while anything larger than 500 Daltons can not. A Dalton, by the way, is is the standard unit that is used for indicating mass on an atomic or molecular scale. Common allergens also tend to be smaller than 500 Daltons.

2. Oil soluble vs water soluble
In general, oil soluble ingredients penetrate much better than water-soluble ingredients because the skin itself is water proof. In technical terms we describe this as the hydrophile or lipophile balance of the ingredient.

A classic example here is a water soluble alphahydroxy acid like lactic acid which works on the surface of the skin. Compare that to a more oil soluble beta hydroxy acid like salicylic acid which can penetrate into pores to fight acne.
This makes sense because much of the intercellular space is filled up with lipids like ceramides.

3. Polarity/charge
Lastly the polarity or the charge of the molecule is also important. For example, both sugar and salt are water soluble but one is polar and one is not so you’d expect them to penetrate differently.

Collectively these properties help determine how likely an ingredient is to penetrate skin. Another factor to consider is the condition of skin itself.

4. The condition of the skin
As we explained a minute ago, skin on some parts of your body is thinner than others. For example the skin under your eye is very thin which is one of the reasons dark circles show up so much. Thin skin is more prone to penetration than thick skin. When you consider the kinetics, if there is less distance it has to penetrate through it makes sense that more could get through.

Also, abraded skin is more susceptible to penetration than intact skin. That means if you’re shaving your face or your armpits, then ingredients are more likely to penetrate deeper into skin in those areas. It also makes sense that this would apply to skin that is heavily exfoliated.

Consider the delivery vehicle

It’s important to consider the formula from which the ingredient is being delivered for two reasons. First, if it’s a rinse off product, it’s unlikely to result in very much penetration. That’s because penetration is measured in milligrams per square centimeter per unit of time. That unit of time is frequently hours not minutes and certainly not seconds. Therefore it is extremely unlikely that anything that is rinsed off the skin will have time to penetrate. A leave on product, like a moisturizing lotion, gives the ingredients much more time to penetrate. (Note: an exception could be ingredients which are highly substantive to skin.)

Second, there may be other ingredients in the formula that enhance penetration. These “penetration enhancers” are typically these either oily materials or ingredients with polyol (OH) groups. They can be chemicals that are either synthetic or natural in origin and they’re thought to work by changing the way the lipids in-between the skin cells are packed together. (Like the “brick and mortar” model we talked about.) Some well known examples include ethanol, some PEGs
, methyl pyrrolidone, 
jojoba oil and peppermint oil. We found a couple of interesting articles on penetration enhancers and we’ll put links to those in the show notes.

Is penetration always a bad thing?

Setting aside for the moment the question of whether or not an ingredient does or does not penetrate the skin there is another important question to ask. If it penetrates the skin is that always bad?

If it just penetrates through the upper layers of skin and is not absorbed into the bloodstream it will eventually just be sloughed off as part of the dead skin cells. To present a systemic hazard it has to not only penetrate the skin but it has to be absorbed from the skin into the bloodstream.

Once in the bloodstream our bodies have a very efficient filtering mechanism in place to remove toxins. This is another reason why concept of the dose makes the poison is so important. Low levels of contaminants will be filtered out by the kidneys and you’ll either come out in your P or feces.

Of course some contaminants can overwhelm the body’s natural filtering system and be hazardous to your health. Lead is a good example – very small amounts of lead are filtered out of your body (that’s one of the reasons it’s okay to have lead in your lipstick) but higher doses of lead do build up in your body and cause health problems.

My point is that the difference between skin penetration and skin absorption is an important distinction.
Its also important to realize that the risk of an ingredient penetrating skin is is factored into the safety assessment done on cosmetic ingredients.

The Beauty Brains bottom line

It’s not easy for ingredients to penetrate through the skin because of it’s “brick and mortar” structure.

An ingredient has to have the right size and the right compatibility with skin lipids to “slip through.”

There are other ingredients called penetration enhancers that boost penetration (especially in transdermal drug patches).

The myths are NOT true about your body absorbing large amounts of chemicals through your skin.

The regulatory bodies that determine the safety of cosmetic ingredients certainly factor skin penetration and absorption into their assessment.


Improbable products

This week we played a special “wake up and smell the bacon” edition of our game. Which of these bacon-themed personal care products is fake? (Listen to the show for the answer.)

  • Bacon scented toilet paper
  • Bacon bit exfoliating scrub
  • Bacon scented deodorant

Comments on this entry are closed.

  • Chris July 21, 2015, 1:59 pm

    Thanks for answering my questions. 🙂

  • amy miranda July 21, 2015, 7:20 pm

    I listened to your episode 92 recording and was pleasantly surprised. Keep up the good work. I also liked the article or post under the recording!! Thank you!

  • Eileen July 21, 2015, 8:27 pm

    Wonderful and highly educational! Now, whenever I hear someone spouting a bunch of bunk about everything being absorbed into the bloodstream, I can refer them to your post. You guys are kind of like the Myth Busters of the cosmetic world–funny, entertaining, knowledgable, educational, and objective. Do I sound like a fan? I am!

    • Randy Schueller July 22, 2015, 8:41 am

      Actually, Eileen, we consider you to be a Super-Fan. Thanks for your continued support!!

  • Kelli July 21, 2015, 10:21 pm

    So glad you guys addressed this!! A lot of people out there believe to much of the “wrong” information they hear. It’s nice to hear from experts who know what they’re talking about.
    I agree with Eileens comment and I am a huge fan of your website also!!

    • Randy Schueller July 22, 2015, 8:42 am

      Thanks Kelli. If it’s not too much trouble we’d really appreciate it if you could help spread the word about us by writing a review on iTunes.

  • amanda July 21, 2015, 10:32 pm

    Thanks for this! It’s very informative. I have a question – if oils are more soluble that water, would it help my serums penetrate them better (and therefore work better) if I mixed them with a little plant oil?

    • Randy Schueller July 22, 2015, 8:43 am

      It’s hard to say Amanda. Some oils are penetration enhancers but it also depends on what’s in your serum. What kind of ingredients are you talking about?

      • amanda July 23, 2015, 11:20 am

        Hi Randy, I use all sorts of serums and essences (I rotate them) with ingredients like – vitamin C, retinol, hyaluronic acid, peptides, stuff with a whole bunch of plant botanicals, brightening ingredients like arbutin, etc. I want to make sure I get the most out of them, so I was wondering if using them with an oil will make them more effective.

        Also, what do you think about using serums/treatments after using a moisturiser. Some Japanese skincare brands recommend using an emulsion/milk before using a serum and moisturiser. I’ve always thought that this would prevent the active ingredients in the serum from penetrating the skin…but they say that it’s actually the reverse, as when your skin is hydrated, it’s in its optimal state to receive the active ingredients. What’s your take?

        • Randy Schueller July 23, 2015, 11:34 am

          Hi Amanda. For many of the ingredients you cited (vitamin C, retinol, hyaluronic acid and peptides) there are data that suggest they really work. Each product you use should be balanced to optimally deliver their active ingredients so I don’t see any benefit from just “using them with an oil.”

          I haven’t seen any data that indicates the order of application of moisturizers makes a big difference. When in doubt, I would apply products containing active ingredients first, then apply the moisturizer. But that’s just my personal opinion.

          I glad you’re finding out website and podcast to be helpful. If you want to help us out you can write a review of our show on iTunes. Perry and I would really appreciate it!

          • amanda July 28, 2015, 8:33 pm

            Thank you so much! This has been really helpful!

  • Wladimir Budnik July 22, 2015, 12:06 am

    Thanks for the excellent and fairly straightforward explanation about penetration of the skin by topically applied substances – bottom line appears to be that penetration is not deep nor substantial. Which poses the question, how do all the antiaging ingredients such as various peptides, plant stem cells and the like used in big brand cosmetics that are advertised both on label and in the media and that supposedly regenerate collagen and elastin, absorbed into the dermis?
    Look forward to your feedback on this one.

    • Randy Schueller July 22, 2015, 8:44 am

      The quick answer is that some of those ingredients are proven to penetrate (at least to deep enough to have an effect.) If you look back at our episodes on peptides and collagen you can find more details.

  • Chris July 22, 2015, 3:59 am

    Here’s an interesting read on Essential Oils as penetration enhancers. Was posted by Liz at the dish forum:


  • gigi July 22, 2015, 8:39 am

    Thanks for the great article! But I have a further question. What about ultrasonic system? Do these types of machines help the penetration? Like what usually the beauticians use. Thanks for the answer in advance.

    • Randy Schueller July 22, 2015, 10:32 am

      Gigi: We have seen some evidence that some devices (particularly the ones that work with electric current) may help penetration of some ingredients. If we find more detailed information we’ll post it here.

  • Judith July 22, 2015, 8:45 am

    That was very informative, thank you! I’m not worried about “chemicals” per say, but I am a bit worried about the retinol penetration. There are some health risks linked with excessive vitamin A consumption.

  • Barbara July 23, 2015, 10:36 am

    I’m sorry but no amount of lead is in lipstick is ok. The sad truth is our bodies are getting overburden with tons of chemicals everyday. Just look at the ingredient list of one product and multiply that by the number of products a person uses each day……scary. Can we trust companies that answer to shareholders and profit to make safe products? Considering it is well known in the industry that these companies self police themselves….

  • Chris July 23, 2015, 3:10 pm

    I’m pretty sure according to you Barbara we should use “greener” products. Well guess what, green products also have chemicals in them. And you are also exposed to those with repeated use. If you really are that worried then you should stop using cosmetics all together but I’m pretty sure that’s not an option.

  • Varsha July 24, 2015, 1:18 pm
    • Randy Schueller July 24, 2015, 2:03 pm

      Thanks Varsha! I clicked the link in the article and that just took me to ANOTHER site that just stated the 60% claim without any support what so ever.

  • Paige July 24, 2015, 9:21 pm

    What about Epsom salt? Does it/can it truly absorb thru the skin? I can’t find any conclusive information online. One expert says yes, another says no. (Thank you for all your hard work and passion.)

  • Zina August 5, 2015, 12:03 pm

    Where are the transcripts? I would like to read the transcript rather than have to listen. Is it possible?

  • Marta Ferreira January 10, 2016, 4:53 am

    You mentioned that AHA’s are not meant to penetrate the skin and I understand that because most products that contain them are exfolliators. But AHA’s, especially glycolic, are also linked to dermal matrix improvement and skin lightning by inhibiting tyrosinase. Do you think that these ingredients are able to penetrate skin when they are present in any product, or does that product need any specific characteristics to improve permeation (besides the lower pH that shifts the molecule to its acid form)?

    • Randy Schueller January 11, 2016, 7:49 am

      Hi Marta. AHA’s have a couple of functions. If they’re just acting as exfoliants on the upper, dead layers of skin then there’s not much need for penetration. If they’re acting on the dermal matrix then they need to penetrate and/or trigger some kind of signaling mechanism to the deeper layers of skin. There are ways to optimize formulas to enhance penetration that would likely be used in the latter example.

      • Marta Ferreira January 11, 2016, 4:25 pm

        Well, in that case an acid toner or serum would be the best, right? And by the way, do you have any idea which concentration would be enough to have anti-aging benefits?

  • Ellie February 7, 2016, 12:24 pm

    hey, I just discovered you guys and I thought this article was amazing, very very informative thank you!!! I just finished grade 12 chemistry, so this was especially interesting to me.

    • Randy Schueller February 7, 2016, 12:41 pm

      Thanks Ellie!

      • Ellie February 8, 2016, 5:14 pm

        I have a question, I have oily acne prone skin and big pores. Does the size of pores affect the penetration of any ingredients?

        • Randy Schueller February 8, 2016, 6:20 pm

          I haven’t seen data on this so I don’t know for sure but my guess is not. Pores are not the major route of skin penetration so I don’t think it makes a difference.

  • jane May 2, 2016, 10:13 pm

    This is helpful for my presentation work on penetration skin of facial mask ingredient but i have some questions to ask.

    For facial mask, is it different from skin care that we use daily? i found that some of them can penetrate our skin for example vit c and e but some cannot. And how is the mechanism they being absorbed into our skin and improve our skin condition? and do facial mask just a temporary effect or our skin can actually absorb those ingredients?

    • Randy Schueller May 3, 2016, 6:48 am

      Is facial mask different from daily products? It depends on which active ingredients are used in each.

      • jane May 4, 2016, 8:16 am

        like nowadays there are lots of mask saying that egg white , snail slime, collagen and etc that can improve our skin condition, but is it the ingredient inside can penetrate our skin? collagen is like too large which can only stay on the surface of our skin and only for temporarily effect right

  • Marc Muller August 30, 2016, 1:57 pm

    Hey Chris,

    Thank you for this article! How deep does the average cosmetic product penetrate the skin? Is it going past the stratum corneum into the lower layers the epidermis? Also some cosmeceutical products claim to penetrate much deeper than general cosmetic products is that the case?

    thank you for your amazing work! Keep it up!

  • Christina Ioanna September 16, 2016, 10:40 am

    Simple and rich, keep it up.

  • sd saxon June 28, 2017, 6:11 pm

    Are there, to your knowledge, a transdermal penetration enhancers that would facilitate the absorption of CBDs into the vascular layer for the medicinal benefit of same? There are those who claim cannabis topicals can relieve joint pain and given the protective nature of the skin, I have my doubts.

    • Randy Schueller June 29, 2017, 7:32 am

      I’m not aware of any such cosmetic technology but perhaps there are drug products that can deliver CBD transdermally.

  • Miguel Acero July 13, 2017, 7:44 pm

    Hi I was wondering if agave nectar would go into the blood stream or any of this ingredients Aqueous Infusion of Agave Teqilana Leaf Extract and Sugar Cane Extract, Pectin, Vegetable Glycerin, Adansonia Digitata Pulp(Baobab) Extract, Cocos Nucifera (Coconut) Oil*, Butyrospermum Parkii (Shea Butter)*, Panthenol (Pro-Vitamin B-5, Aloe Barbadensis Leaf Extract*, Tocopherol (Vitamin E – Vegetable Oil Source), Linum Usitatissimum (Linseed/Flax) Seed Extract, Hibiscus Sabdariffa Extract, Potassium Sorbate, Proprietary Essential Oil Because agave nectar has a lot of sugar and I don’t want to be unhealthy I only use this product on my hair from shea moisture it’s a curling gel please it would mean a lot to know your answer !!!!

    • Randy Schueller July 14, 2017, 7:16 am

      There is no scientific reason to believe that using this product will penetrate and do any harm to you.

  • Sarah August 4, 2017, 3:04 am

    Hi, I know this is an old post but I am trying to find out if hydrogenated oils penetrate the skin, in particular hydrogenated coco glycerides. There is plenty of info about the 500 Dalton rule on the internet but I can’t actually find a list of ingredients along with their molecular weights so that I can determine the penetrations. Any ideas on the safety of hydrogenated oils if applied to the skin?
    Many thanks for the article.

  • Ashley August 31, 2017, 6:43 pm

    Are essential oils something that our skin is able to absorb? Penetrating deep enough to have any effects?

  • Susan September 5, 2017, 2:07 am

    I have tried many of the so called pain patches with absolutely no relief. Is there any topical pain relief product that you have found to actually work?

  • Anju Soni October 17, 2017, 1:18 pm

    Does aloe Vera and rose water works inside the skin…

  • Parisa October 17, 2017, 7:39 pm

    Wonderful job! Thank you! Could you please explain the obsorption ( % of penetration) of essential oil by skin?

  • Anna February 27, 2018, 6:40 pm

    Thank you for the informative information. I just wanted to know if by any chance say eyeliner particles penetrate the skin what would happen to it. As what you said earlier would it just sloughed off or by any chance would it be stuck between lasers of skin and stay there . thank you so much.

    • Perry Romanowski March 12, 2018, 3:15 pm

      I doubt it would get stuck in between the layers of skin. If this happened frequently it would be a big problem for cosmetics.

  • Alihsan March 1, 2018, 1:28 am

    Hi! İ’m Alihsan.
    Mr.Schueller İ want to ask a question about vitamin penetration.
    İ wonder how efficency a vitamin ( especially,A,D,E,K oil base vitamins) works in a moistrizing body cream that has the main claim is Vitamin Cream for your vitamin deficiency
    İ want to read some article about this creams absorbtion but i thought maybe you may give some clue about this topic.
    Best Regards.

    • Perry Romanowski April 3, 2018, 8:14 am

      Vitamins typically don’t penetrate the skin enough to have a significant effect.

  • Suzanne Hall December 8, 2019, 7:52 pm

    I’d love to see a fact-based article about estrogenic ingredients – should some people avoid them? are they more of a problem transdermally than through ingestion?