[1] It is caused by prolonged exposure to irritants, leading to direct injury of the epidermal cells of the skin, which activates an immune response, resulting in an inflammatory cutaneous reaction.

Symptoms of both forms include the following: While either form of contact dermatitis can affect any part of the body, irritant contact dermatitis often affects the hands, which have been exposed by resting in or dipping into a container (sink, pail, tub, swimming pools with high chlorine) containing the irritant.

[9] Common causes of allergic contact dermatitis include: nickel allergy, 14K or 18K gold, Balsam of Peru (Myroxylon pereirae), and chromium.

[12] Common causes of irritant contact dermatitis include solvents, metalworking fluids, latex, kerosene, ethylene oxide, paper, especially papers coated with chemicals and printing inks, certain foods and drink,[13] food flavorings and spices,[14] perfume,[13] surfactants in topical medications and cosmetics, alkalis, low humidity from air conditioning, and many plants.

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); and alkalis (drain cleaners, strong soap with lye residues).

Allergic contact dermatitis (ACD) is accepted to be the most prevalent form of immunotoxicity found in humans, and is a common occupational and environmental health problem.

[17] The process of skin sensitization begins when a susceptible subject is exposed to the allergen in sufficient concentration to elicit the required cutaneous immune response.

This causes sensitization and when exposure to the same allergen at a later time at the same or different skin site leads to a secondary immune response at the point of contact.

[17] Sometimes termed "photoaggravated",[18] and divided into two categories, phototoxic and photoallergic, PCD is the eczematous condition which is triggered by an interaction between an otherwise unharmful or less harmful substance on the skin and ultraviolet light (320–400 nm UVA) (ESCD 2006), therefore manifesting itself only in regions where the affected person has been exposed to such rays.

For this reason, this form of contact dermatitis is usually associated only with areas of skin that are left uncovered by clothing, and it can be soundly defeated by avoiding exposure to sunlight.

Since contact dermatitis relies on an irritant or an allergen to initiate the reaction, it is important for the patient to identify the responsible agent and avoid it.

[20] The patch tests were based on the concept of a type IV hypersensitivity reaction where there is exposure of allergens to skin and checking for the development of contact dermatitis in that area.

[21] The top three allergens found in patch tests from 2005 to 2006 were: nickel sulfate (19.0%), Myroxylon pereirae (Balsam of Peru, 11.9%), and fragrance mix I (11.5%).

[24] Using histology on its own is insufficient, as these findings have been acknowledged not to distinguish,[24] and even positive patch testing does not rule out the existence of an irritant form of dermatitis as well as an immunological one.

In an industrial setting the employer has a duty of care to its worker to provide the correct level of safety equipment to mitigate exposure to harmful irritants.

[26] If the rash does not improve or continues to spread after 2–3 of days of self-care, or if the itching and/or pain is severe, the patient should contact a dermatologist or other physician.