Dermatitis is a catch-all term for a group of skin conditions that exhibit a rash. Generally these rashes are the result of some sort of allergic reaction, and dermatitis can be separated into groupings based on what type of allergen the response is caused by. Eczema is probably the best known type of skin condition in this category, and is more properly referred to as eczematous dermatitis. Treatment is dependent on the precise type, although generally avoiding the allergen once it is identified will help the rash clear up eventually.

The outward appearance of the skin condition depends on a number of factors, including the type, where it is present, how severe it is, and how long it has been present. The one common symptom to the entire category is that it is itchy, and all types are also characterized by redness of the skin. Additionally, the condition may cause blisters, scaling of the skin, and crusting over of the skin. The borders of the rash may be quite striking, or they may gradually fade into the surrounding skin tone.

One of the most common types of rash is allergic contact dermatitis, which is caused by topical exposure to an allergen of some sort. Common allergens include certain plants, fragrances found in perfumes or lotions, and certain clothing materials. An allergic reaction can be tested for by making use of a patch test, where a small amount of the allergen is rubbed on a small area of exposed skin, to see if a rash forms. One widely-used patch test is the True Test, which tests for twenty-nine distinct allergens.

Another common type of condition is seborrhoeic dermatitis, or cradle cap, often referred to simply as dandruff. Generally this condition is found on the scalp and parts of the face, and it may sometimes be found in the groin or on the chest as well. It is the result of the skin reacting to the yeast Pityrosporum, and as a result it is relatively-easily treated by using an antifungal agent, generally added to a shampoo. It may also be treated with anti-inflammatory agents.

Autosensitization dermatitis is yet another type, often caused by a yeast reaction somewhere on the body. Unlike many types of dermatitis, this type is not a direct reaction to an antigen or yeast, but is rather a sympathetic response. When the autoimmune system responds particularly strongly somewhere on the body, often to yeast outbreaks, a rash may break out on an entirely different area of the body as a side effect of the primary response.

Exposure to a variety of chemical irritants can also result in skin conditions of this type. Many people notice a rash develop if they spend extensive time in a chlorine-loaded swimming pool, for example, or if they are cleaning with heavy-duty cleansers and using insufficient protection. Most cleaning chemicals, as well as chemicals used in metal working, painting, and wood treatment, can cause this type of skin condition, which is why rubber gloves and other protective garments are generally recommended.

Depending on the type of dermatitis, treatments may vary, but there are a few treatments widely used. For basic cases, most people simply use an antihistamine of some sort, to make the itching subside until the rash itself disappears. It is also a good idea to take care of any other rashes on the body, since they can often be causing secondary rashes. For more severe rashes, a doctor may prescribe some sort of topical steroid.