Contact dermatitis occurs in two major forms: allergic contact dermatitis and irritant contact dermatitis. These conditions are all related to items that encounter your skin from the outside. These are not related to ingesting certain foods or having seasonal allergies.
Allergic contact dermatitis is related to contact allergens that your body just doesn’t like, and causes it to mount an immunologic reaction to get rid of it. It typically presents with blistering, but sometimes can be as subtle as a dry skin rash. Poison Ivy and nickel used in metals (i.e. earrings, belt buckles) are some of the most well known examples. Not everyone will form a rash to these substances.
Irritant contact dermatitis, on the other hand, is created from exposure to products that create an irritation to the skin, such as chemicals. Anyone with enough exposure to these products will form a rash. It commonly presents as inflamed, dry, rough and cracked skin, but can also be as abrupt as bright red patches to the more severe chemicals. Detergents used in more aggressive household cleaning products are a common culprit.
The first line of treatment for both conditions is to eliminate the causative agent, which can often times eliminate the condition. Skin testing for allergens can be performed for the more difficult cases. Topical and systemic (i.e. oral) medicines are the most common forms of treatment. Light therapy and wound care are also needed in more severe cases.