• Poison ivy, oak, and sumac: Poison ivy and oak are common culprits of allergic contact dermatitis during the summer time. The sensitizing allergens are pentadecylcatechol and heptadecylcatechol which are found in the sap of these plants. Sensitivity to poison ivy, oak and sumac results in sensitivity to the other plants in the same family which would include cashews, mango and lacquer trees.
• Iodine: Iodine preparations are widely used in antiseptics. The degree of allergic contact dermatitis caused by iodine varies depending on the type of preparation. A study by Lee et al tested iodine in petrolatum, iodine in 70% isopropyl alcohol and povidone-iodine. It was found that when iodine was complexed with povidone, less subjects developed dermatitis.
• Nickel: Nickel sensitivity is typically seen in women wearing nickel earrings. Nickel is also found in the buttons of jeans, costume jewelry and wrist watches. It is important to note that although stainless steel used in some jewelry has nickel, it is so tightly bound that it usually does not cause an allergic reaction.
• Rubber: The most frequent rubber allergens are mercaptobenzothiazole and thiuram. Shoes and gloves are the most common causes of allergic contact dermatitis by rubber. The reaction will usually be limited to the hands or feet in a patchy distribution where there has been direct contact to the rubber.
• Certain topical medications: Benzocaine 5% (cross reacts with Para-aminobenzoic acid (PABA)-containing sun screen), Neomycin Sulfate 20%, Ethylenediamine 1 % have all been documented as possible causes of allergic contact dermatitis.
• Cosmetics: An allergy to a specific ingredient or ingredients in a product is usually present. Paraphenylenediamine is a dye found in permanent hair coloring. Sensitization to paraphenylenediamine occurs in hairdressers and in clients who have their hair colored. When completely oxidized, as the dye on a fur coat, paraphenylenediamine is no longer a source of allergic contact dermatitis.

Presentation:
The rash is often very itchy. The appearance of the rash depends on the stage. In the acute phase, one would expect to see red patches and fluid-filled bumps (vesicles) with oozing; swelling may also be present. In the chronic phase we would expect longer term changes such as crusting, thickening, and scaling.

Diagnosis:
The diagnosis is usually made clinically. A detailed history of occupation, hygienic habits, and hobbies is frequently necessary to find the culprit. The causative agent for allergic contact dermatitis may be identified by a patch test. In fact, patch testing is the only way to differentiate an irritant contact dermatitis and allergic contact dermatitis. Clinically and even under a microscope, they cannot be reliably distinguished. In patch testing, multiple different chemicals are applied to patches which are taped onto a the back of the patient. The patches are then removed after 48 hours and interpreted by a dermatologist at 48 and 96 hours. Patch testing is indicated in the following cases: 1) diagnosis is in doubt, 2) rash does not respond to treatment, 3) rash recurs.

Treatment:
Wearing protective clothing, and avoiding the contact allergen are the two most important ways to prevent further dermatitis. One should also avoid frequent water exposure as it will dry and chap the skin. Moisturizing plays a key role in aiding the skin's natural healing.

For symptoms, astringent dressings or soothing baths reduce weeping and itching while oral histamines often help the itch. Cool tap water compresses are useful if vesicles are present. Topical steroids generally aid in diminishing the inflammatory reaction that causes all of the symptoms associated with contact dermatitis. Dermatologists will frequently use a topical steroid for therapy in mild to moderate rashes. Systemic steroids may also be used for severe cases.

References:   

J. Bourke; I. Coulson; J. English: Guidelines for the Management of Contact Dermatitis: an Update. The British Journal of Dermatology. 2009; 160(5):946-954   

S. K. Lee; H. Zhai; H. I. Maibach: Allergic contact dermatitis from iodine preparations: a conundrum. Exog Dermatol 2002;1:238-24