Contact dermatitis can mean many things to many very itchy people. The American Academy of Allergy, Asthma and Immunology describes this condition as having a "broad ranges of reactions." Allergic contact dermatitis is caused by the direct contact of the skin with any substance that results in an allergic reaction. This could mean a man-made allergen, such as the scent used in a fabric softener, or a natural allergen, such as a plant to which the individual is sensitive.
Inflammation
Contact dermatitis results when the body responds to contact with a seemingly harmless foreign substance as if it was a potential threat. This is what occurs in allergic reactions. The cells respond to the foreign substance, or allergen, by releasing histamines, chemicals which increase the permeability of blood vessels. As the blood vessels become more permeable and blood flow to the affected area increases, fluids containing white blood cells leave the blood vessels and enter the area where the contact with the allergen has occurred. This results in swelling, itchiness, warmth and redness referred to as inflammation.
Reactions to the allergen may not be immediate. Some cases of allergic contact dermatitis do not show symptoms until 24 to 48 hours after contact with the allergen has occurred.
The degree of inflammation varies on a case by case basis. Some cases of contact dermatitis may be mild and brief, other can be extremely uncomfortable and complicated by the individual's compulsion to scratch the affected area.
Skin Lesions
Lesions such as blisters or pimple-like bumps can occur where the skin has made contact with an allergen. Contact with the leaves of Toxicodendron radicans, more commonly known as poison ivy, causes a skin reaction which is characterized by the blistering associated with allergic contact dermatitis.
Skin lesions caused by contact dermatitis can open up and drain, oozing serous fluid and eventually crusting over. Scratching of the affected area is to be avoided, as the introduction of bacteria into the affected area can cause secondary infection, according to Medline Plus, a website of the National Institutes of Health.
Photosensitivity
Photocontact dermatitis occurs when certain substances come in contact with skin that is subsequently exposed to the sun. Cosmetics such as sunscreens and perfumes are often the culprit in cases of photocontact dermatitis. The symptoms of photocontact dermatitis include inflammation, rashes and lesions, but only in areas that have both come into contact with the allergen and been subjected to sun exposure, according to the Asthma and Allergy Foundation of America.
