Contact dermatitis is a rash caused by the skin coming in contact with something they have a reaction to. There are two broad types of contact dermatitis: allergic and irritant contact dermatitis.
Allergic contact dermatitis:
Allergic contact dermatitis occurs in persons who have become allergic to a substance from previous exposure causing the skin to develop bumps, swelling, blisters, itch or thickening on the area that was in contact with the substance. Common sources are nickel, fragrances, rubber, cosmetics, preservatives, cobalt, neomycin. It happens after several hours to days of exposure.
Irritant contact dermatitis
Irritant contact dermatitis is not an allergy but a reaction to irritation to a substance that results in physical, chemical or mechanical trauma. Common irritants include detergents, acids, solvents, abrasive materials . The skin can become swollen, red, wet and oozing or dry and thick.
How is contact dermatitis diagnosed?
Your doctor can help you determine if you have contact dermatitis by going through a thorough history with you regarding exposures. A physical exam of the skin helps determine if the rash is new or old and if they have peculiar shapes or distributions (eg. a V-shaped rash on the top of the feet in patients allergic to rubber slippers, or a rash around the finger where a ring is used).
If it is unclear if you have an allergy causing the rash, specialists may want to do a patch test (see TRUE.com) in order to help narrow down or confirm potential contact allergies.
How is it treated?
The primary treatment is avoidance of irritants and allergies that can be identified, hence the importance of determining the cause when possible. Skin tends to be more sensitive if it is raw/cracked or thin (eg.eyelids, groin, top of hands) so avoidance in these particular areas is key (hence, if the eyelids are already affected, avoidance of use of makeup in those who are allergic is best). Your doctor can help you find the proper creams/ointments to place on the eruption and sometimes pills (such as antihistamines) can relieve the itch. In some instances, oral steroids are antibiotics are warranted for very severe eruptions or those that become infected from scratching.