In the workplace, irritant contact dermatitis can develop after a short, heavy exposure or a repeated or prolonged, low exposure to a substance. The appearance of irritant contact dermatitis varies considerably according to the conditions of exposure. For example, an accidental contact with a strong irritant causes immediate blisters. Contact with a mild irritant may only produce redness of the skin. However, if the irritation continues, small lesions or sores appear on the reddened area; afterwards crusts and scales form. The skin damage usually heals a few weeks after exposure ends if no complications have arisen (e.g., no infections occurred).
The irritant action of a substance depends on its ability to change some properties of the outer layer of the skin that acts as a protective barrier against toxic substances. Among other changes, some substances can remove skin oils and moisture from the outer layer of the skin. This reduces the protective action of the skin and increases the ability of irritants to enter or infiltrate the skin. The removal of fat or fat-like material from the skin is also responsible for the dryness, cracking and whitening of the skin.
To produce the damage, the irritant substance must infiltrate the outer layer of the skin. Following infiltration, the substance comes into contact with cells and tissues. The substance also reacts with certain chemicals naturally present (endogenous) in cells and tissues. These reactions produce skin damage. The body's first reaction to the damage is a localized acute inflammation. The cells and tissues try to repair the damage and set up a defensive response to remove the invading material causing the damage. During the body's defensive response phase, a person may experience pain, warmth, redness and swelling in the irritated area.
Minimal skin damage, as in the thickening of the inner layer of the skin, will not be visible. However, when the damage is severe, the skin shows signs of chapping, scaling, and blistering. Some skin cells also die. Typically, an irritant reaction develops within a few hours from exposure and is at its worst after approximately twenty-four hours.
Source: Canadian Centre for Occupational Health and Safety (CCOHS) www.ccohs.ca