The skin absorbs virtually any chemical that touches it, new research shows. This overturns the traditional view that it keeps out most substances. Some chemicals, such as the aromatherapy oil Coumarin, are 60 per cent absorbed when they lie on the skin.
Scientists at St Mary's Hospital Medical School in London have developed a model that uses a sample of fresh human skin at 32xC supplied with fluids to keep it viable. They have found wide variation in the extent to which chemicals are absorbed - but some of the chemical always gets through.
Sheila Hotchkiss and colleagues have now tested about 30 substances. "It's just a question of how much and how quickly," said Dr Hotchkiss, lecturer in biochemical toxicology. "What I'm worried about is occupational exposure or exposure to chemicals in the garden."
Dr Hotchkiss found that most absorption happens within the first half hour. A layer of skin, the stratum corneum, which is half the thickness of paper, absorbs the chemical quickly and stores it like a reservoir, gradually releasing it into the body below. So washing chemicals off immediately is essential. Two aromatic amines used frequently in factories, MDA and MbOCA, were absorbed to the same extent whether left on for 30 minutes or 24 hours.
Dr Hotchkiss has found that for some chemicals, the skin is "far more important as a route" than is breathing it in.
The scientists found that cinnamaldehyde, which imparts a cinnamon smell to products such as soap, is 29 per cent absorbed. Phenol, a disinfectant mainly used in industry, which may be toxic, is 19 per cent absorbed. Even chemicals designed to be washed off immediately, such as shampoo, can be absorbed in the short time they touch the skin.
Speaking after a conference at Imperial College London, she said that more research was needed into the harm these chemicals do once they have been absorbed.
Dr Hotchkiss said gloves should always be worn when using household chemicals. Aromatherapy oils, which can be highly concentrated, should be properly diluted and washed off immediately if used in a massage. Covering up after coming into contact with a chemical can make matters worse because it prevents evaporation.