Tuesday, March 6, 2012

What the heck is a penetration enhancer?

Some people would have you believe that everything can penetrate the upper layers of your skin - the epidermis - and make it into your bloodstream, creating all kinds of problems and "poisoning us from the inside out". They will argue that nicotine and estrogen patches prove their case that things that go on our skin are absorbed into our body or bloodstream. (As a note, they're wrong. Do you know how much effort and science goes into making those things? It's not as easy as rubbing some tobacco or a yam on your skin to get nicotine or estrogen into our blood!) Our skin is an amazingly good preventer of things penetrating to lower levels of the skin, so we often have to use something like a skin penetration enhancer to get a product or ingredient to do more than sit on top of the upper layer of the stratum corneum.

So 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)

In other words, a skin penetration enhancer alters the physical or chemical nature of the stratum corneum - top layer of our skin - to allow certain things to penetrate this layer to reach the lower layers of skin. This does not mean the ingredient in question will end up in our blood stream - as you can see, it's a long way from the surface of your skin (the stratum corneum) down to the subcutis, where we find the circulation system. (For more information on your skin, click here).

Why would we want to have something penetrate the upper levels of our skin? It's nice to have our humectants go a little lower into our skin to increase moisturization. In the case of AHAs, exfoliating from under the skin leaves our skin looking fresher and newer. And there are some cosmeceuticals that need to get lower than the first few layers of the stratum corneum to work well.

How do penetration enhancers work? Wow, you've asked quite the complicated question there! "Within the intercellular route, enhancers may interact at the polar head groups of the lipids, within aqueous regions between lipid head groups, and between the lipophilic tails of the bilayer. Inside the corneocyte it is the keratin fibrils and their associated water that are the targets. High concentrations of solvents may also alter partitioning processes. Because of the involvement of lipid and protein modifications, together with partitioning phenomena, the scheme of possible enhancer interactions has been termed the Lipid Protein Partitioning (LPP) theory. This theory is applied specifically to water, Azone, dimethylsulphoxide, dimethylformamide, 2–pyrrolidone, N-methyl-2–pyrrolidone, oleic acid, decylmethylsulphoxide, sodium lauryl sulphate and propylene glycol." (Reference)

Or a slightly shorter version of this..."It is generally agreed that the SC intercellular lipid domain is the site of action for many chemical penetration enhancers." (Reference) (Here's a post on this very topic!)

In other words, penetration enhancers work by interacting with the stratum corneum lipids. (If you want to know even more about this topic, click on the two references above!)

What are some penetration enhancers we find in our products? There's a fantastic list you can find here (click for link), but some of the most well known are propylene glycol, IPM, IPP, eugenol, linalool, basil oil (reference), ibuprofen (thanks to the eugenol and acetyl eugenol), possibly Vitamin E, sodium lauryl sulfate (SLS),

How much should we use to get the skin penetrating effects? "Skin penetration enhancing effects are, to some extent, specific and dependent on the drug, vehicle, enhancer concentration and probably other factors." (Reference) We need to figure out how much of something we need to work with other things. For instance, 2% of something might not act as a penetration enhancer and 5% might. It's hard to know these things without researching every single ingredient for this one piece of information - and it's hard to find that information, to be honest. If you read some sites, you'd think that even looking at propylene glycol will result in gobs of it running through your veins, but we know that a titch isn't going to do it for us. And some things will inactivate the penetration enhancers, so we have to really know our ingredients and how they will work with other ingredients!

Penetration of our skin isn't a bad thing or a good thing, it's just a thing. This doesn't mean that these ingredients are bad, although a lot of natural or health food sites would have you believe this. It just means that there is the potential to get some ingredients to penetrate deeper into our skin (or be absorbed by our skin) when we use ingredients like SLS or propylene glycol. It might be a good thing if you want more moisturization in the lower levels of the epidermis or it might be a bad thing if your husband sat on a discarded estrogen patch and didn't realize it for a few days! As with anything in chemistry, the dosage is what is important!

If you want to make a good argument about how we know not everything penetrates our skin, ask those people who are convinced that we absorb 5 pounds of make-up a year how much they weigh after a nice bath. Do they weigh more after a long soak? How much do they gain after eating a hamburger and chips with their hands?

Of course they don't weigh more - our skin is very good at keeping the outside world outside. Can you imagine what would happen after a freak rain storm or after you played in the snow? If our skin lets in every molecule it touches, then I should be 1/10 water and 4/10 body wash, 3/10 sugar scrub, and 2/10 chocolate!

*Side note: You have no idea what kind of web pages come up when you google the phrase "penetration enhancer", which really shows you how committed I am to researching things for this blog!

References and further reading:
Skin penetration enhancers: Friend or Foe? (Personal Care Truth.) Great information about how deep things will penetrate our skin.
Skin penetration enhancer list (Dow Corning)


Tara said...

Hi Susan. This comment isn't related to today's post, but I am wondering if you have any interest in writing a post on the infamous Whole Foods "unacceptable ingredients" list. It seems so ridiculous, but I think a lot of formulators are trying to hold themselves up to these "standards". It really is confusing to me why many of the ingredients are on the list, but I have not researched the reasons behind it. Just a thought :-D

Susan Barclay-Nichols said...

Hi Tara! I thought I had done this, but I can't find it in a search, so I guess I haven't. Do you have a link to a copy of the list? I had one, but I can't find it now either (although I admit I'm a bit sleepy from all the muscle relaxants for my toasted shoulder). Can you send it to me (sjbarclay@telus.net)? What a great idea for a post!

Lise M Andersen said...

Ooh I love the comment about checking weight after a bath--- excellent point Susan!

Nedeia said...

Thanks thanks thanks, Susan! Great post, reading it for the third time now :)

Tara said...

Hi Susan. Here is the link to Whole Foods' unacceptable list of ingredients in body care products:

Tara said...

Sorry for posting here. My iPad is unpredictable at sending emails :-S

Nancy Liedel said...

It would be shorter to have an, "Acceptable Ingredients," list. Even things the Natural Products Association accepts, Coco Betaine, are a no-no to Whole Foods. Who just appear to have copies the EWG's list and said, "ThIS IS PERFECT!! LET'S STEAL IT!"

I find it all so distasteful, it's not worth trying and our local rep that introduces products to the company, does not have the time of day for any cottage industry. She wants big, and NATURAL! Where do you think some of the larger companies get these genius marketing ideas? I know someone, a friend, who sat at a Society of Cosmetic Chemists dinner and this guy from a large company, was telling her all about how they were going to release shampoo bars and no, she did not get it, surfactant shampoo bars.

This is a woman who is known for her surfactant shampoo bars. Not that they would make it, but larger companies are watching small ones. It happens all the time. They get ideas from us, and voila, present to Whole Foods, who suddenly sees the light.

Sadly, by their reviews, the light is the front of an oncoming train.

Rant off :)

DuhBe said...

And now back to the penetration enhancers... (BTW -the term makes me cringe)

I was just re-reading Leslie Bauman's skin type solutions last week and her take on these is very interesting. If you have sensitive skin, she suggests avoiding these ingredients because sensitive skin is already pretty permeable. But for those with resistant skin, she suggests they seek out products with those ingredients. So once again - you can see why some people vehemently argue an ingredient is bad while others thinks it's awesome. We all have different skin. Mine skin is sensitive so I choose to leave all the p. enhancers out of my ingredient cabinet completely.

Microformulations said...

I am a Consultant Formulator in the Personal care Industry and I echo your frustration with Whole Foods. The list doesn't even touch on their new "standards" which are not realistic.

In the past I worked with a client to develop an "Organic" Shampoo for Whole Foods. They specifically demanded no thickeners (even Xanthan Gum), no colorants and no fragrances. They loved the result and in fact I still see it on the shelf at Whole Foods. HOWEVER, as a perfectionist I am not proud of the product. What we developed was a brownish, oily smelling shampoo that poured like water and didn't clean as well as I would have liked.

I did get to see the hurdles that Whole Foods will place in your way. Their Administrative demands are more so than even the US Government. They will task you with several hours per product for documentation. Then after all is done, it will come down to simply what the cost per ounce is and how low can you go.

In my experience Whole Foods is not the "Golden Goose" that everyone makes it out to be. They will wave their 300 stores at you, but realistically most products will be only purchased regionally.

In my belief, I see the biggest opportunity now for dedicated Natural Products. A little known fact is that the big manufacturers will use the Botanicals and EO's at label claim levels (oftentimes 0.05% wt/wt) rather than the effective levels. I have several clients now that value the homeopathic qualities of these products and use them correctly. There are several outlets for these products, but take my word, Whole Foods is not one of them.

I work everyday with Cosmetic Entrepreneurs to get their products into the Market. The bulk of Cosmetic innovation is being done at the "hobbyist" level and I try to get it on the shelf.

DrJohn said...

Would be great if you follow up with your take on penetration encapsulating vehicles like liposomes, solid lipid nanoparticles, that sort of thing. Thanks.

Will said...

ROTFLMBO re penetration enhancer and internet search.

I do love research!

All jokes aside, especially thanks for this post. I've read much of what you wrote when researching for my first facial product (and reverse engineering a bit), but having all the info assembled in one place in a coherent order helps a lot.

Have a great day!


Magdalena Keating said...

Hey Susan, I am getting into this stuff and can't wait to learn more about penetration enhancers. I am looking for penetration enhancers from natural origins = can you suggest any? Also the link referring to basil oil being a penetration enhancer is broken - do you happen to have any more info on this one?

All the best of the best


Magdalena Keating said...

Hey there Susan,

I am learning more and more about making my own products. I have been making face creams for a little while now (still ultra newbie though) and am coming to understand that I need to use some sort of penetration enhancer. I wanted to stick with 'natural origin' ingredients (I know you cringe when someone says that) :)

I wanted to experiment with making a face cream using B3 and wondered whether linalool would be a good penetration enhancer to use? Do you or have you come across any recipes that use Linalool or basil oil as a penetration enhancer?

Have a great day!


Susan Barclay-Nichols said...

I've updated the basil link.