Contact dermatitis is a type of skin inflammation that occurs when you come into contact with certain substances. Typically, the skin becomes red, sore, swollen, oozy, or crusty.
There are two types of contact dermatitis: irritant and allergic.
Irritant Contact Dermatitis
Irritant contact dermatitis is the most common form of contact dermatitis. It makes up 80% of cases in the United States. This type occurs when substances directly injure the skin. It usually looks like a burn. It is most common on the hands and forearms, but can occur on any part of the body.
Substances that commonly cause contact dermatitis include:
- solvents, such as turpentine and kerosene
- fabric softener
- hair dye
- weed killers
- rubber gloves
- wet diapers
- various chemicals
Jobs that require frequent exposure to heat and water—such as food preparation, dishwashing, and hairstyling—can make skin more prone to irritant contact dermatitis.
Phototoxic contact dermatitis is a form of irritant contact dermatitis in which the irritant is only activated after exposure to ultraviolet (UV) light as in sunlight. This is common with perfumes and coal tar.
Allergic Contact Dermatitis
Allergic contact dermatitis (ACD) occurs when your immune system reacts to a substance to which you are allergic. Your skin may become itchy, red, scaly, or raw. You may develop blisters that weep, ooze, or become crusty.
Common allergens that result in contact dermatitis include:
- adhesives used for false eyelashes and toupees
- antibiotics applied to the skin
- nail polish
- hair dye
- metals, such as those in watch straps, jewelry, zippers, buttons, and clasps usually containing nickel
Photoallergic contact dermatitis is a form of ACD in which the substance only becomes sensitizing after exposure to UV light. This is typical of aftershave lotions, sunscreens, and topical sulfonamides.
In some cases, ingestion of a substance after topical sensitization can cause widespread dermatitis. For example, diphenhydramine (Benadryl) may be used on the skin to relieve itching. If sensitization occurs, taking Benadryl orally may then cause dermatitis. This is called systemically induced ACD.
The allergic reaction that causes allergic contact dermatitis is not the same as most allergic reactions. In most allergic reactions, your immune system creates IgE antibodies to fight substances believed to be harmful.
Allergic contact dermatitis is a type IV cell-mediated hypersensitivity reaction. It is also called delayed type hypersensitivity. It does involve the immune system, but no IgE antibodies are created. Instead, T cells are sensitized to respond to the substance you are allergic to. This reaction has two phases.
An allergen is a substance that you are allergic to. Your first exposure to an allergen the sensitization phase of the reaction. In this phase, T cells are sensitized to the allergen. This means that they learn to recognize it and attack it. This process may take from only six days to as much as several years. The time it takes depends on the substance. Strong sensitizers, such as poison ivy, take only a few days. Weak sensitizers, such as fragrances, may take several years. This is why you may “suddenly” develop ACD after using the same product for several years with no problem.
Allergic Response After Reexposure
After sensitization is complete, exposure to the substance will cause an allergic reaction. The sensitized T cells activate and release cytokines and other inflammatory cells that cause the inflammation and rash of ACD.
Contact dermatitis can be very uncomfortable and unsightly. In some cases, it might become infected. Most cases clear up in two to three weeks. The rash is likely to return if you come in contact with the substance again. If you have photoallergic contact dermatitis, sun exposure may cause your symptoms to flare for many years. This is called a persistent light reaction.
Powerful drugs: Treating allergic reactions has become somewhat more effective with use of new medications. The best strategy, however, is prevention. Stay away from known allergens and irritants, in order to keep irritation and even more significant symptoms from developing in the first place.