Areas of the body such as the forearms, which may be particularly hairy, are most easily penetrated by chemicals since they can enter down the small duct containing the hair shaft. Chemicals can also enter through cuts, punctures or scrapes of the skin since these are breaks in the protective layer. Contact with some chemicals such as detergents or organic solvents can cause skin dryness and cracking. There can also be hives, ulcerations or skin flaking. All these conditions weaken the protective layer of the skin and may allow chemicals to enter the body.
Chemicals can vary enormously in the degree to which they penetrate the skin.
Some solvents such as trichloroethylene, naphtha and toluene may soften the keratin layer but are not believed to penetrate much further unless there is prolonged skin contact. On the other hand, chemicals such as benzene, carbon tetrachloride, carbon disulfide and methyl alcohol can readily pass through the epidermis and subsequently enter the blood stream. Some chemicals are so corrosive they burn holes in the skin, allowing entry for infection or other chemicals. In some instances, chemicals may enter by accidental injection through the skin. This may occur in hospital settings or in industrial hole-punching or injection processes.