Molecular Aspects in Allergic and Irritant Contact Dermatitis

Abstract

Skin exposure to chemicals, natural or synthetic, may result in adverse reactions ranging from mild irritation to cutaneous allergy. These inflammatory reactions, subsequent to chemical exposure, derive from very different biological mechanisms. For a chemical to be a sensitizer, it must have the ability to bind to protein so that a non-self-antigen can be produced. The evidence indicates that normally this binding occurs by covalent bond formation. From a chemical point of view, chemical sensitizers can be divided into three categories: haptens that can react directly with nucleophilic side chains of amino acids, prohaptens that need an enzymatic (biotic) transformation to become reactive haptens, and prehaptens that need a nonenzymatic (abiotic) chemical transformation such as air oxidation to become reactive haptens. Molecular mechanisms associated with irritant contact dermatitis are more difficult to investigate and are very often based on reversible interactions with biological systems. Irritant contact dermatitis (ICD) describes a multifactorial disease involving endogenous and exogenous factors resulting from exposure to irritants. It is a direct response of the skin to chemicals and does not require prior sensitization. With sufficient concentration or duration of exposures, a wide range of molecules is capable of acting as irritants. The properties of the irritating substance as pH, solubility, or detergent action and its physical state as gaseous, liquid, or solid are important to approach the molecular mechanisms associated with ICD. However, it is possible to highlight interactions between the skin and irritant, mainly surfactants, which result in ICD.