Tuesday, March 6, 2012
What the heck is a penetration enhancer?
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)
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)
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!
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)