On Monday, we took a look at hydrogenation, whether it can turn an oil into a trans fat, some naturally occurring trans fats, and, finally, if hydrogenated thingies are bad for our skin, and on Tuesday, we took a look at the molecular structure of oils and plastics. Today, let’s move on to the second paragraph in Maty’s Are hydrogenated oils bad for your skin? post, which is all about how long it takes something to absorb into our skin and equating food with skin care products.
It takes 26 seconds for something to absorb into your skin…
“While there may not be a ton of research regarding the effect of hydrogenated oils when applied topically, we know it only takes 26 seconds for something to absorb into your skin. So if you wouldn’t put it in your mouth, why put it on your skin? We think you’d want to treat it the same way as the food you put into your body.” (Quoted from this page.)
And I found this one, “As a wellness consultant, I would not recommend using personal care products containing hydrogenated oil. Our skin is the largest bodily organ. Like the rest of our organs, the skin absorbs every substance that comes in contact with it.” (Link)
I have to comment about this last sentence. All our organs absorb every substance that comes in contact with them? I don’t know where to start with how wrong this is, so I’ll just leave it here…
I always love the “there’s not a lot of research” comments because it’s a sure sign that the writer is fearmongering. I find that, when challenged, they respond with comments like, “It’s just common sense,” or “Do your own research” or something else that puts the onus on the challenger to prove them wrong. This isn’t the way science works. If someone makes a statement, it’s up to them to provide the evidence.
What are the questions we need to ask ourselves here? What does “absorption” mean? What’s the role of our skin? Does it absorb everything it touches? If it does, how does that work? If it doesn’t, how does that work? Do we want our skin to absorb everything it touches? Do we want it to absorb anything at all?
Quick aside: We’ll be using a lot of information from the skin chemistry & skin types section of the blog and this post, the chemistry of our skin (overview).
QUICK DEFINITION OF PENETRATION VERSUS ABSORPTION!
Penetration is when a molecule is applied to the skin and penetrates through to the bottom layer of the epidermis, the stratum basale. Remember that the epidermis is the top layer of the skin and does not have any vasculature for the molecule to be absorbed into the bloodstream. Thus, the molecule does not have an affect on any body systems. When a molecule is absorbed, this means that the molecule has reached the dermis where there is vasculature. (Reference, and it’s a good one!)
We’re defining penetration as a molecule penetrating the stratum corneum or upper layers of the skin (the epidermis)
We’re defining absorption as a molecule being applied to the skin and making it through the stratum corneum and all those layers in the epidermis to make it into the dermis, where we find blood and making it to the dermis where we find blood vessels.
In this picture to the left, the epidermis is the upper layer of skin that makes up about 1/5 of it, while the dermis makes up the rest.
As a note, cosmetics, by definition, would not be absorbed into our skin to reach the bloodstream. Something that does this would be considered a drug. I could mic drop here and say I’ve proved my point, but that wouldn’t be much fun, eh?
Let’s get started on these questions by consulting a few reputable references!
WHAT’S THE ROLE OF SKIN?
“The skin keeps vital chemicals and nutrients in the body while providing a barrier against dangerous substances from entering the body…” (Merck Manual, Consumer Version)
“The skin is a vital organ that covers the entire outside of the body, forming a protective barrier against pathogens and injuries from the environment. The skin is the body’s largest organ, and it is only about 2 mm thick. It shields the body against heat, light, injury, and infection. The skin also helps regulate body temperature, gathers sensory information from the environment, stores water, fat, and vitamin D, and acts as a physical barrier in protecting us from diseases.” (Skin Structure and Function)
“The epidermis, the outermost layer of skin, provides a waterproof barrier and creates our skin tone.” (WebMD)
It’s pretty clear that the skin’s number one job is to act as a barrier between us and the outside world with all its potential perils. If this is the case, wouldn’t absorbing “something” in 26 seconds or “every substance that comes in contact with it” be the sign of a malfunctioning skin barrier?
I could offer more references, but they all say the same thing – skin = barrier. If you’d like more, I can provide them, but I really would encourage you to do a search for this topic yourself as there’s so many interesting things to learn!
DOES SKIN ABSORB EVERYTHING IT TOUCHES OR ABSORBS EVERYTHING IN 26 SECONDS?
Oh, no. Wait a minute! Is that why my feet are burgundy and green with something that looks like an atom of some sort? Clearly I’ve been absorbing every substance that’s come in contact with them! Better switch to my sushi socks immediately!
No. I think it’s abundantly clear that your skin doesn’t absorb every substance applied to it within 26 seconds and both of these comments are completely ludicrous. To be able to say this with a straight face goes against our own powers of observation to notice basic things, like putting something on our skin and watching it not be absorbed.
This can be disproved in a few minutes by reading a textbook or doing a search online. (I wrote a bit about it here…)
Skin is most assuredly not “our body’s greatest sponge”. Your skin’s job is to protect the rest of your body from the outside world as a barrier. If you’re absorbing everything that touches it in 26 seconds, I’m sad to say that you’re this close to imminent death and should be living in one of those bubbles, although I’d worry that every time you touched the bubble, you’d be absorbing the stuff it’s made from and you’d still die pretty horribly.
LET’S EXPERIMENT WITH OUR SKIN PERMEABILITY!
Let’s think about this idea rationally. If my skin absorbed every substance with which it comes in contact, I should have cotton, nylon, rayon, wool, and other fabric embedded in my skin after years of wearing clothes and sleeping on sheets.
I should have remnants of all the eye shadow I’ve worn in my lifetime tattooing my eye lids with all kinds of crazy colours.
I should be able to get rip roaring plastered by rubbing vodka into my skin. Alcohol in the bloodstream will make me drunk and register in tests regardless of method of ingestion.
My fingertips aren’t stained permanently with nacho cheese dust.
My Facebook post that not everything is absorbed by your skin last year ended up with months of being followed around by two women who were calling me all kinds of names for months – uptight, sexless, idiotic – and one even went to so far as to call Voyageur Soap & Candle to have me fired as a teacher for stating a biological fact. I did like the one woman who said she’d be telling everyone in her “sphere of influence” to boycott me and Voyageur because I stated a biological fact. This same woman showed up on Unicorn Chemist’s post on not infusing oils to say as women, we should be lifting each other up, not pulling each other down, so I posted the screenshot about her sphere of influence, and she stopped commenting. The moral of this story – don’t be a jerk online to someone who takes screenshots of jerks she encounters on line…
Okay, so I think I’ve made the case that not every substance is absorbed by our skin, but are there some things that might be? Yes!
SKIN ABSORPTION & PENETRATION
Yep, some things penetrate our skin and others can be absorbed, but it’s not as easy as they make it seem. Either way, these things can bust a hole in that barrier that can cause problems. (I’ll address this in a few minutes…)
When this conversation arises, someone always asks, “What about various patches – like nicotine or estrogen – that can be applied to our skin to deliver medication?” Those are pharmaceutical products that took years, millions of dollars, and serious chemical know how to create. It’s not as simple as rubbing a cigarette on one’s arm to get the same effect. In fact, the existence of these patches demonstrates how hard it is to have something bypass skin’s barrier protection.
IF SOMETHING CAN PENETRATE OR BE ABSORBED BY THE SKIN, HOW DOES IT DO IT?
The quick summary is that there are different pathways a substance can take to penetrate our skin and be absorbed…
From this paper: “The topic is complex as skin structure is heterogeneous and because there are a number of penetration routes through the stratum corneum barrier: the intercellular, intracellular and follicular pathways. Recent advances in the study of penetration mechanisms deal with the control of the intercellular penetration route by the crystalline state of lipids, and the penetration through skin appendages (the follicular pathway) that appears to contribute much more than was previously thought.”
I found this amazing blog, which seems to have only been active a short while, geek + makeup + wisdom by a cosmetic chemist, and they have two really great posts that might interest you. Crash course in skin biology is full of great information on our skin. Skin penetration: An Overview is a fantastic explanation of how things might penetrate our skin.
THE 500 DALTON RULE
If something is small enough, it might be able to penetrate through the skin barrier.
“Human skin has unique properties of which functioning as a physicochemical barrier is one of the most apparent. The human integument is able to resist the penetration of many molecules. However, especially smaller molecules can surpass transcutaneously. They are able to go by the corneal layer, which is thought to form the main deterrent. We argue that the molecular weight (MW) of a compound must be under 500 Dalton to allow skin absorption. Larger molecules cannot pass the corneal layer. Arguments for this “500 Dalton rule” are; 1) virtually all common contact allergens are under 500 Dalton, larger molecules are not known as contact sensitizers. They cannot penetrate and thus cannot act as allergens in man; 2) the most commonly used pharmacological agents applied in topical dermatotherapy are all under 500 Dalton; 3) all known topical drugs used in transdermal drug-delivery systems are under 500 Dalton. In addition, clinical experience with topical agents such as cyclosporine, tacrolimus and ascomycins gives further arguments for the reality of the 500 Dalton rule. For pharmaceutical development purposes, it seems logical to restrict the development of new innovative compounds to a MW of under 500 Dalton, when topical dermatological therapy or percutaneous systemic therapy or vaccination is the objective.” (The 500 Dalton rule for the skin penetration of chemical compounds and drugs.)
We find some ingredients are smaller than 500 Daltons, like some of our amino acids or components in proteins. Could they penetrate our skin? They could, but the size of a molecule isn’t the only determinant of whether something can penetrate or be absorbed by the skin. There are a number of other variables, such as pH, concentration, solubility, and ionic charge. (Again, I can’t suggest this post enough as it’s just excellent.)
WHEN SOMETHING IS ABSORBED BY OUR SKIN, IT CAN PUNCH A HOLE IN THE BARRIER, WHICH ISN’T NECESSARILY A GOOD THING.
I’ve written about penetration enhancers* many times before – what the heck are penetration enhancers? – but let’s do a quick recap!
*Do not do a search for this topic with “safe search” off as you will find all kinds of things you can’t unsee!
What do skin penetration enhancers* do? “Skin penetration enhancers reversibly decrease the barrier resistance of the stratum corneum and allow drugs to penetrate more readily to the viable tissues and the systemic circulation.” (Reference)
Here’s another definition: “…a skin penetration enhancer increases skin permeability by reversibly damaging or by altering the physiochemical nature of the stratum corneum to reduce its diffusional resistance.” (Reference)
As you can see in both references, increasing penetration means decreasing the skin’s barrier protections, which can lead to irritation, skin conditions, and other issues.
DO WE WANT THINGS TO PENETRATE OR BE ABSORBED BY OUR SKIN?
Cosmetics mainly stay on the top of our skin to moisturize, hydrate, condition, and generally make our skin feel nicer. There’s no need for a lotion to do more than that. In fact, I can’t see any good coming from the emollients, humectants, and such being absorbed into our bloodstream. So when it comes to absorption, my answer is a definite no! (Plus, these would be drugs, not cosmetics, and we don’t make drugs in our workshop.)
What about penetrating into our skin? I think there could be a case made that having certain ingredients penetrating into our stratum corneum to exfoliate – like alpha hydroxy acids – or hydrate – like (possibly) ultra low molecular weight hyaluronic acids – might be a good thing, but we run the risk of annoying your skin barrier and causing irritation. Just think about what happens
Ingredients like alpha-hydroxy acids and salicylic acid can penetrate our skin’s epidermis, but don’t absorb into the bloodstream.
We don’t need ingredients to penetrate our skin to be effective – after all, glycerin sits on the top of our skin and it’s an excellent hydrator while our cationic ingredients are substantive and conditioning – and most of them won’t, which, is pretty much a good thing.
Related posts:
If Vitamin C doesn’t penetrate the skin, what is the benefit of it?
Can oils penetrate our skin? (updated)
Can polyphenols found in oils penetrate our skin? (updated)
Can phytosterols found in oils penetreate our skin? (updated)
LET’S RECAP…
“While there may not be a ton of research regarding the effect of hydrogenated oils when applied topically, we know it only takes 26 seconds for something to absorb into your skin. So if you wouldn’t put it in your mouth, why put it on your skin? We think you’d want to treat it the same way as the food you put into your body.” (Quoted from this page.)
It doesn’t take “26 seconds for something to absorb into your skin”. I’m not sure how they came up with this number, but it is a strange and arbitrary period of time that has nothing to do with anything scientific.
“As a wellness consultant, I would not recommend using personal care products containing hydrogenated oil. Our skin is the largest bodily organ. Like the rest of our organs, the skin absorbs every substance that comes in contact with it.” (Link)
Our skin doesn’t “absorb every substance that comes into contact with it,” and, in fact, it’s pretty much the opposite. We have to make a serious effort to have our skin absorb something through the dermis and into the bloodstream. We can demonstrate this is wrong in our own homes by putting something on our skin and watching if it is absorbed.
Thank you for joining me for this quite lengthy post that contains a lot of my ranting. Let me know what you think in the comments! I’m always up for debates, and really enjoy links and more science, so give me what you gots!
If this post interested you, don’t forget to check out the skin chemistry & skin types section of the blog (find it under the “resources” tab in the menu).
Join me tomorrow for the final part of this rant as we look at this sentence, “if you wouldn’t put it in your mouth, why put it on your skin?”