Irritant contact dermatitis occurs when chemicals or physical agents damage the surface of the skin faster than the skin is able to repair the damage. The dermatitis or eczema is often well demarcated with a glazed surface but there may be redness, itching, swelling, blistering and scaling of the damaged area. This may be indistinguishable from other types of dermatitis. The severity of the dermatitis is highly variable and depends on many factors including:
- Amount and strength of the irritant
- Length and frequency of exposure (eg. short heavy exposure or repeated/prolonged low exposure)
- Skin susceptibility (eg. thick, thin, oily, dry, very fair, previously damaged skin or pre-existing atopic tendency)
- Environmental factors (eg. high or low temperature or humidity)
Irritants include such everyday things as water, detergents, solvents, acids, alkalis, adhesives, metalworking fluids and friction. Often several of these act together to injure the skin. Irritants damage the skin by removing oils and moisture from its outer layer, allowing the irritants to penetrate more deeply and cause further damage by triggering inflammation.
Irritant contact dermatitis may affect anyone, given sufficient exposure to irritants, but those with atopic dermatitis are particularly susceptible. 80% of cases of occupational hand dermatitis are due to irritants, most often affecting cleaners, hairdressers and food handlers.
Allergic contact dermatitis may look similar to irritant contact dermatitis, but it is caused by an immune response following skin contact with an allergenic substance. Tiny quantities may be sufficient to cause allergy, whereas a certain minimum exposure is necessary for irritant contact dermatitis. Irritant and allergic contact dermatitis may coexist.
Pompholyx eczema (dyshidrotic eczema) may also be difficult to distinguish. In this condition, there are itchy clusters of blisters along the sides of the fingers and on the palms, often triggered by sweating.
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