The Weiss Skin Institute established a Contact Dermatitis Clinic to help patients who suffer from skin allergies. You can develop skin allergies to almost anything including metals, rubbers, nail polish, plants, and even the ingredients in skin care products and topical medications. Many persistent rashes like hand eczema, eyelid dermatitis, and facial rashes are due to repetitive contact with a particular substance that you may not even realize. If the source of the allergy is not isolated with the TrueTest, Dr. Weiss will use Finn chambers, to attempt to isolate the allergenic source. Because of this advanced methodology, the Weiss Skin Institute is frequently used as a regional referral source for patients with contact dermatitis.

What is contact dermatitis?
Contact dermatitis is an inflammatory response of the skin to an antigen or irritant. There are two types of contact dermatitis, allergic contact dermatitis and primary irritant dermatitis. Allergic contact dermatitis affects only individuals previously sensitized to the contactant. An allergic reaction is specific to the individual and to a substance (or a group of related substances) called an allergen. Allergy is a hypersensitivity (oversensitivity) to a particular substance, and always involves the immune system. All areas of skin that are in contact with the allergen develop the rash. Primary irritant dermatitis results from direct injury to the skin. It affects individuals exposed to specific irritants and generally produces discomfort immediately following exposure.

How does allergic contact dermatitis occur?
Allergic contact dermatitis is a cell-mediated, type IV, delayed hypersensitivity reaction that results when specific antigens enter under the skin. This means that the offending substance to which you are allergic combines with a special receptor and travels to the second layer of skin, the dermis, where the immune cells (T cells) become sensitized. The next time that you are exposed to the antigen, the allergic reaction takes place.

What are the common causes of allergic contact dermatitis?
The most common offenders in allergic contact dermatitis are plants of the Toxicodendron genus (e.g., poison ivy, poison oak, poison sumac). Other substances include nickel sulfate (various metal alloys), potassium dichromate (cements, household cleaners), formaldehyde, ethylenediamine (dyes, medications), mercaptobenzothiazole (rubbers), thiuram (fungicides), and paraphenylenediamine (dyes, photographic chemicals). Irritant contact dermatitis occurs when an irritant produces direct local toxic effect on the cells of the top layer of skin, with a subsequent inflammatory response in the second layer of skin (dermis).

Where is irritant contact dermatitis most likely to present?
The most common site for irritant contact dermatitis is the hand. Individuals with atopic dermatitis are genetically predisposed to develop irritant contact dermatitis especially of the hands. Although irritant contact dermatitis is caused mostly by chemicals (e.g., acids, alkalis, solvents, oxidants), plants (e.g., hot peppers, garlic, tobacco) also have been implicated. Severity of the reaction is related to the amount and duration of exposure to the irritant.

How does allergic contact dermatitis present?
In acute allergic contact dermatitis, lesions appear within 24-96 hours of exposure to the allergen. The main symptom, in addition to the rash, is itching.

How come I only get a rash when I am in the sun?
This is called photodermatitis. Photodermatitis is diagnosed by the presence of lesions limited to sun-exposed body areas. There are two types of reactions that are considered part of the photodermatitis family: the first is a phototoxic reaction in which burning is the primary complaint. The other is a photoallergic reaction in which itching is the main complaint.

How do you test if my rash is a contact dermatitis?
The Weiss Skin Institute performs patch testing to diagnose the cause of skin allergies. Patch testing is different than the prick testing performed by an allergist to diagnose hay fever or food allergies. In patch testing, small amounts of substances, without needles, are placed in patches and applied on the back for 48 hours. Then, a reading of the patches is conducted to see if any skin allergies exist.

How do you patch test?
Small amounts of the most common substances to which patients are allergic are placed on small patches applied to your back. We reinforce these with tape because they need to stay in place for 48 hours. During these 48 hours you are not allowed to exercise or shower. You then return to our office after 48 hours so that we may remove the patches and see if there were any positive reactions.

What if I have a positive test?
We will discuss where this substance that caused a reaction is found and how you may avoid it in the future.

Are there treatments for contact dermatitis?
The primary treatment is to avoid the substance. To treat an acute flare, however, you are often prescribed a topical steroid or other topical immune modulator.