Contact dermatitis or Irritant dermatitis is a term for a skin reaction resulting from exposure to allergens (allergic contact dermatitis) or irritants (irritant contact dermatitis). Phototoxic dermatitis occurs when the allergen or irritant is activated by sunlight.

Introduction

Contact dermatitis is a localized rash or irritation of the skin caused by contact with a foreign substance. Only the superficial regions of the skin are affected in contact dermatitis. Inflammation of the affected tissue is present in the epidermis (the outermost layer of skin) and the outer dermis (the layer beneath the epidermis). Unlike contact urticaria, in which a rash appears within minutes of exposure and fades away within minutes to hours, contact dermatitis takes days to fade away. Even then, contact dermatitis fades only if the skin no longer comes in contact with the allergen or irritant. Contact dermatitis results in large, burning, and itchy rashes, and these can take anywhere from several days to weeks to heal. Chronic contact dermatitis can develop when the removal of the offending agent no longer provides expected relief.

Causes

In North/South America, the most common causes of allergic contact dermatitis are plants of the Toxicodendron genus: poison ivy, poison oak, and poison sumac. Specific plant species that can induce such contact dermatitis include Western Poison Oak, a widespread plant in the western USA. Common causes of irritant contact dermatitis are harsh (highly alkaline) soaps, detergents, and cleaning products.Tea tree oil is a known suspect.

Types of contact dermatitis

There are three types of contact dermatitis: irritant contact, allergic contact, and photocontact dermatitis. Photocontact dermatitis is divided into two categories: phototoxic and photoallergic.

Chemical irritant contact dermatitis

is either acute or chronic, which is usually associated with strong and weak irritants respectively (HSE MS24). The following definition is provided by Mathias and Maibach (1978): a nonimmunologic local inflammatory reaction characterized by erythema, edema, or corrosion following single or repeated application of a chemical substance to an identical cutaneous site.

The mechanism of action varies between toxins. Detergents, surfactants, extremes of pH, and organic solvents all have the common effect of directly affecting the barrier properties of the epidermis. These effects include removing fat emulsion, inflicting cellular damage on the epithelium, and increasing the transepidermal water loss by damaging the horny layer water-binding mechanisms and damaging the DNA, which causes the layer to thin. Strong concentrations of irritants cause an acute effect, but this is not as common as the accumulative, chronic effect of irritants whose deleterious effects build up with subsequent doses (ESCD 2006).

Common chemical irritants implicated include solvents (alcohol, xylene, turpentine, esters, acetone, ketones, and others); metalworking fluids (neat oils, water-based metalworking fluids with surfactants); latex; kerosene; ethylene oxide; surfactants in topical medications and cosmetics (sodium lauryl sulfate); alkalies (drain cleaners, strong soap with lye residues).