The Facts Behind Skin Absorption
November 9, 2011
2 comments
@ Skin Forum
Professor Hadgraft, an expert in transdermal absorption at the London School of Pharmacy, is getting increasingly frustrated with false statements in womens’ and life style magazines and web sites.
“The skin is the largest organ of the body and absorbs 70% of the topically applied products!”
These statements are often substantiated by references to experiments on rodent or rabbit skin which are totally inappropriate. Other discussion members add that:
- These articles are written in response to new product launches and become no more that an advertising opportunity.
- The journalists are bedazzled by the hype presented by marketing.
- If scientists were to contribute to the information packs then these false statements would never have seen the light of day.
The Facts Behind Skin Absorption
- The skin possesses an outer layer, stratum corneum, which is a very impressive barrier. It is about one sixth the thickness of a piece of paper but stops us losing excessive water because of its unique structure.
- The stratum corneum has a structure of a brick wall, the skin cells – keratinocytes – are the bricks. If the bricks are bigger, the path any active ingredient has to go through when penetrating into the skin is longer, if smaller, the path is shorter.
- The “mortar” layer is an organised structure of orderly hydrophilic and hydrophobic domains. Actives soluble in water, eg. vitamin C, cannot penetrate into the lipophylic layer and oil soluble actives eg. vitamin A and E, cannot penetrate into water soluble layers. Actives soluble both in oil and water perform best.
- Absorption is variable depending on: the skin site and its condition, the properties of the active applied, the product in which the active is applied. Absorption is usually higher in the face than on the body; it is related to the cell size. Cheek corneocytes are small and the protease activity is higher on the cheek than forearm, leading to more penetration.
- For most of ingredients the percent of dose absorbed is around 1-2%. For some it is less than 0.1% For some, very few, it is 10-20%.
- The barrier properties of the skin and the subsequent low absorption of actives into the skin are a major problem in the topical treatment of skin diseases! The majority of active ingredients that have potential to affect the biology of the skin are rarely delivered in amounts to allow them to realise that potential!
Source: Skin Forum on LinkedIN and Inaugural SCS Lecture October 2011
Categories: Skincare Formulation, Skincare Research
absorption, active ingredients, media, myths, skin research, transdermal
