The term "dermatitis" refers to inflammation of the skin, which causes redness, itching, or scaling. One form is contact dermatitis, which occurs when the skin comes into contact with a substance. This substance may be either an allergen, causing an allergic reaction, or an irritant, causing direct damage to the skin. There are two main types of contact dermatitis: irritant and allergic.

Irritant contact dermatitis is the most common form, accounting for about 80% of cases. It occurs when the skin is exposed to substances that irritate it chemically, mechanically, or physically, damaging its natural barrier. This form usually results from everyday products such as soaps and cleaning agents. Although anyone can develop irritant dermatitis, individuals with pre-existing skin conditions or dry skin are more vulnerable. On the other hand, allergic contact dermatitis occurs when the skin comes into contact with an allergen that activates the immune system and causes inflammation. This type may be triggered by allergens such as nickel in jewelry, perfumes and cosmetics, as well as substances like rubber or chemicals found in shoes. Certain medications, such as hydrocortisone, antibiotics, and benzocaine, may also cause allergic contact dermatitis. In some cases, laundry detergents may also be responsible.

The acute phase of contact dermatitis is characterized by intense itching, redness, and small blisters that may rupture and release fluid. If the condition becomes chronic, the skin may become dry, scaly, and change in texture or color. The rash is usually confined to areas of the skin that came into contact with the allergen, although it may spread to other areas if the allergen is transferred there, for example, via the hands.

The rash typically appears within 12 to 48 hours after exposure to the allergen, although in some cases it may be delayed and appear up to two weeks later. In rare cases, the rash may persist for months or even years, making it difficult to identify the cause of the reaction.