Although the skin is waterproof, other substances can permeate the epidermis. Skin patches have been around since the 1970s - for instance, to help people quit smoking in nicotine replacement therapy. But gels that introduce drugs through the skin are also available. These techniques use an alcohol base to deliver substances into the bloodstream - hormones or painkillers, for example. Oil-based cosmetic creams can only penetrate the outer layers of the epidermis, and so have no effect on the living cells deep beneath the skin surface.
Did you know?
* Dermis is the Greek word for skin
* For every square inch of skin you have:10 hairs;100 sweat glands; 1m blood vessels
* Skin sheds between 30,000 and 40,000 cells a minute (cells pictured below)