Mechanisms of irritant contact dermatitis

Abstract

Irritant contact dermatitis is an eczematous reaction in the skin of external origin. In contrast to allergic contact dermatitis, no eliciting allergens can be identified. The spectrum of irritant reactions includes subjective irritant response, acute irritant contact dermatitis, chronic irritant contact dermatitis, and chemical burns (Table 1). Irritant contact dermatitis is in its acute form characterized by erythema, infiltration, and vesiculation. In its more chronic form, dryness, fissuring, and hyperkeratosis are more pronounced. It is thus clear that the clinical reaction pattern of mild to moderate irritant contact dermatitis is often indistinguishable from the allergic contact dermatitis reaction. Thus, differentiation between these two reaction types is often based solely on patient history and skin allergy tests. Despite the common hallmarks of irritant contact dermatitis, the clinical manifestation of the skin lesions developing following contact with different irritants varies. Factors that may influence the outcome of skin contact with irritants can be divided as follows: □Exogenous: such as structural and chemical properties of the irritant, exposure to other irritants, and environmental conditions, e.g., temperature and humidity. □Endogenous: such as body region that is exposed (the scrotum is much more sensitive than, e.g., the upper back), age [1], race [2], and pre-existing skin disease. Moreover, in addition to the capacity of different irritants to induce clinically different reactions, it has been reported that marked interindividual variation in the threshold for eliciting clinical irritant reaction in skin is present [3]. In the past, the pathogenesis of irritant contact dermatitis was thought to be nonimmunological. However, today it is generally accepted that the immune system plays a key role in eliciting irritant reactions. This has been underscored by human and animal studies demonstrating the importance of signal molecules, e.g., cytokines, in eliciting the irritant reaction.