Mechanisms of irritant and allergic contact dermatitis

Contact dermatitis describes the skin reaction resulting from exposure to irritants (irritant contact dermatitis) or allergens (allergic contact dermatitis). In most patients, irritant and allergic contact dermatitis (ACD) are clinically indistinguishable. Also histopathologically, no distinguishing markers have been identified. This is in line with the fact that in irritant and ACD, principal inflammatory pathways are essentially similar. The pivotal different factor in ACD is the involvement of allergen-specific T cells as initiators of the inflammatory skin reaction. In irritant contact dermatitis (ICD), the inflammatory reaction mainly depends on either or both chemical and physical irritation. The most frequent chemical irritative factors are long - lasting and repetitive contacts to water, detergents, solvents, or a combination of these factors, often aggravated by too high or too low humidity. Inflammatory reactions to irritants are not triggered by one specific substance or cause, and do not show rapid amplification of severity by repeated insults and are thus called unspecific.