July 2005

An 11-year-old male presents to your office with a complaint of a rash on both of his arms and itching. He was playing baseball in the park with his friends three days ago and thinks he may have retrieved the ball from some bushes a couple of times.

He started itching the night before last, and yesterday he noticed a rash on his arms which seems to be “spreading.” The itching has become worse. He has tried some calamine lotion without relief.

What do you think is the diagnosis?

Answer

This child has an allergic contact dermatitis. The allergen in this case is urushiol, which is found in the sap of poison ivy, poison oak and poison sumac. Allergic contact dermatitis to urushiol is one of the most common reactions to an allergen in the United States. Following exposure to the urushiol, the dermatitis can appear in 12 to 48 hours somewhat dependent on the intensity of exposure and the sensitivity of the patient.

In children, exposed areas are the most affected, ie, arms, legs and face (see related photos below). Linear lesions can be noted comprised of erythema, edema and/or vesicobullous lesions. When the contact is airborne (for example, burning of leaves and twigs, campfires, and fireplace fires), the dermatitis may appear more diffuse with involvement especially of the face and arms with widespread erythema and edema, swelling of the eyelids, fine vesicles and weeping of the involved areas. Most often, exposure occurs following direct contact with the allergen; however, the urushiol can be carried on fur of pets, clothing and sports equipment.

Following exposure to urushiol, it is best to quickly remove as much of the allergen as possible through washing both the skin and clothing with running water. Stibich et al conducted a study which showed that post-contact prevention of allergic contact dermatitis with either a surfactant (an ultra dishwashing soap) or an oil-removing compound was not statistically different than the use of a chemical inactivation product (which was more expensive).

Source: Patricia Treadwell, MD

One common myth concerning urushiol dermatitis is that the lesions spread by scratching. In fact, the urushiol itself can be spread if an individual has the allergen on their hands. After the dermatitis has developed, the fluid in the vesicles actually does not spread the dermatitis. Areas which have been exposed to less allergen may erupt over a few days as the individual’s immune system becomes activated.

Once the dermatitis has developed, mild cases may be treated with cool baths or showers and over-the-counter calamine lotion or drying solutions. More moderate cases require prescription strength potent topical corticosteroid preparations and antihistamines. Severe cases or cases with significant facial involvement may require oral corticosteroid preparations for a 10- to 14-day course. As usual, screening questions regarding HIV status, tuberculosis exposure and varicella immune status should be completed prior to prescribing the medication.

Preventing urushiol dermatitis by avoiding contact with the allergen is the best approach.

For more information:

• Allen PL: Leaves of three, let them be: if it were only that easy! Pediatr Nurs. 2004;30:129-135.
• Oka K, et al: A study of cross-reactions between mango contact allergens and urushiol. Contact Dermatitis. 2004;51:292-296.
• Stibich AS, et al: Cost-effective post-exposure prevention of poison ivy dermatitis. Int J Dermatol. 2000;39:515-518.