Contact dermatitis refers to a reaction of the skin to something that comes into contact with the skin. When a skin rash occurs due to such exposure, it is termed a contact dermatitis. There are two types of contact dermatitis: irritant contact dermatitis and allergic contact dermatitis.
Irritant contact dermatitis is what happens when your skin is exposed to multiple irritating chemicals, like excessive hand washing, dry skin with sweat in the winter, over scrubbing of the skin or using a new product with an ingredient that causes inflammation.
Allergic contact dermatitis is caused by a true allergic reaction to a specific chemical. Sometimes it is a chemical in something applied to the skin ( like a fragrance or a preservative in a skin cream or cleanser) and sometimes it comes from something that causes periodic contact (like nickel in jewelry, hair dye or rubber).
Contact dermatitis looks like eczema- it is usually dry, red and scaly itchy. It may be obvious what is causing it but usually it isn't, requiring some detective work to identify what the culprit it.
The most important factor in the treatment of contact dermatitis is identification of the offending agent and avoiding contact with that agent, or irritating substances. Treatment will usually involve topical corticosteroid applications, and in severe situations, systemic treatment may be initiated. Future exposure to the causative agent will generally result in a recurrence of the contact dermatitis, so avoidance is key.