Dermatitis is a catch-all term for a group of skin conditions that cause a rash. These rashes are typically, but not always, the result of an allergic reaction. Types of dermatitis include eczema and dandruff, as well as those caused by allergies. Appropriate treatment depends on the precise cause of the condition, but often includes either an oral or a topical medication. In most cases, avoiding triggers once they are identified will help the rash clear up over time.
Symptoms depend on a number of factors, including the location, severity, and duration of the reaction. The most common are an itchy rash and reddened skin, although dry flaky skin, blisters, scaly skin, and crusty lesions may also occur. The rash might have sharply-defined borders, or it might gradually fade into the surrounding skin tone, depending on the cause.
Types of Dermatitis
One of the most common types of rash is allergic contact dermatitis, which is caused by the skin being exposed to an allergen. Common allergens include certain plants, perfume and lotion fragrances, and fabric treatments and dyes. An allergic reaction can be screened for with a patch test, where a small amount of the relevant substance is rubbed on an area of exposed skin and watched for a reaction. One widely-used patch test is the True Test, which screens more than 30 distinct allergens, including various types of mold and pollen. Reactions can develop anywhere on the body that has been exposed to the allergen.
Seborrhoeic dermatitis, another common condition, is usually referred to as dandruff — or cradle cap when it occurs in infants. It most often develops on the scalp and parts of the face but can sometimes appear on the groin or chest. Dandruff is, in part, the result of the skin reacting to one of a family of yeasts called Malassezia, combined with excess production of skin oils. In most cases, it is easily treated with an antifungal agent, such as an over-the-counter anti-dandruff shampoo.
The signs and symptoms of eczema can resemble those of a contact allergy, but they stem from different causes. Although many people with eczema are also affected by seasonal allergies or asthma, this condition is caused by skin hypersensitivity rather than by an allergic reaction. A hypersensitivity reaction is one in which the immune system reacts strongly but non-specifically to a wide variety of substances, causing skin redness and irritation, and often blisters. Eczema is a chronic condition, and can be worsened by exposure to rough fabrics, chemicals, cold or dry air, sudden temperature changes, and other irritants. Stress can also cause a flare-up of symptoms.
This term refers to skin irritation that is triggered by a skin infection, but is not directly caused by it. Often, the cause is a yeast or fungal infection. For example, sometimes a primary infection with Tinea pedis, the fungus which causes athlete’s foot, can cause a secondary rash to develop elsewhere on the body. When they occur, these secondary rashes tend to appear between one and three weeks after the original infection and typically present with more severe symptoms.
Dermatitis can be caused by exposure to a variety of chemical irritants, including acids, bases, and solvents. Strong chemicals can rapidly cause dangerous burns, but diluted ones often lead to irritation. Many people notice a rash develop if they spend extensive time in a chlorine-loaded swimming pool, for example, or if they are using heavy-duty cleaners without sufficient skin protection. Most cleaning chemicals, as well as chemicals used in metalworking, painting, and wood treatment, can cause this type of skin condition, which is why rubber gloves and other protective garments are generally recommended.
Treatment and Prevention
The root cause of the various types of dermatitis is an immune reaction that draws immune cells and molecules to the contact location. The release of immune chemicals called histamines is largely responsible for the characteristic itchiness and redness. Most treatments are therefore aimed at controlling the immune response to the triggering agent.
Treatments may vary, but some are commonly used for a range of rashes. For mild cases, an antihistamine medication is usually enough to allow the itching to subside until the rash itself heals. For more severe or chronic rashes, a medical professional might prescribe a topical steroid; however, because steroids are a broad-spectrum immune suppressant, these medications are for short-term use only. Many people find they are able to reduce or eliminate contact with the irritants that caused the rash, preventing further problems. In some cases, such as with eczema, exposure cannot be completely controlled, and long-term or even lifelong monitoring and treatment is necessary.