Allergic contact dermatitis associated with the workplace develops in stages. There is a period during which an individual may be continually in contact with allergenic substances without developing any skin reaction. This can last a lifetime or only a few days. The allergenic action of a substance depends on its ability to change some properties of the outer layer of the skin. This layer acts as a protective barrier against toxic substances.
Some substances can remove fats, oils and water from the outer layer of the skin.
These substances diminish the protective action of the skin and make it easier for substances to penetrate the skin. The skin allergy really begins with a process called sensitization. It starts with the penetration of allergenic substances into the outer layer of the skin. The process lasts from four days to three weeks. During this period there are no signs of skin damage.