Ask the OnCall+ Experts: Allergies

Answer: Scabies is caused by an infestation of the skin by the mite Sarcoptes scabiei. Transmission of scabies is usually from person to person by direct skin contact. They can survive off a host for 24-36 hours or even longer in colder, humid environments. It is not common, but there have been authenticated reports of scabies being contracted by wearing or handling heavily contaminated clothing or by close contact with bed linens on which an infested individual has slept. Symptoms, primarily itching, typically begin three to four weeks after infestation. In patients who have previously been infested with scabies, symptoms may start within one to three days after reinfestation.

The reason for the "return" of the scabies may be due to incomplete treatment. First-line treatments for adults include topical permethrin cream or oral ivermectin. Household and close personal contacts must be treated simultaneously.

Immediately after treatment, all bed linens and clothing worn by the patient within the past several days need to be washed in hot water and dried in a hot dryer, sent to the dry cleaners, or bagged in plastic bags for a couple of weeks. The itching from the scabies may persist for two to three weeks after successful treatment. Thus, persistent itching does not necessarily indicate persistent or recurrent infestation.

Ivermectin is a single-dose oral treatment, which is usually repeated two weeks later. Ivermectin is not recommended for pregnant or lactating women or children below 15 kilograms.

If using permethrin cream, it must be applied on all body parts from the neck down, including the area under the nails. In children and older adults, the hairline, temples, neck and forehead should be treated. The cream has to remain in place at least eight hours before washing off. Permethrin is usually a single-application treatment but may be repeated in two weeks if there is still evidence of live mites.

If one of the above treatment regimens has been meticulously followed, and the individual again contracts scabies, it would more than likely be a new infestation.

- Dr. Dana Wallace, Vice President, American College of Allergy, Asthma & Immunology (ACAAI)


Question: What is the best treatment for poison ivy?

Answer: Poison ivy is a contact dermatitis caused by the plants of the genus Toxicodendron (which means "poisonous tree"). Urushiol is the allergic agent in the toxic oil (oleoresin) of the poison ivy plant.

If the oleoresin is washed off within 10 minutes, 50 percent can be removed. Intense itching and redness of the skin followed by bumps and blisters usually develop within 48 hours of skin contact with the toxic oil. While the initial rash usually occurs in the area of skin contact with the oleoresin, subsequent lesions develop in remote body areas due to the systemic allergic response. The fluid from the blisters does not "spread" the rash.

Treatment consist of oral antihistamines and topical soothing lotions, such as calamine lotion. For milder cases, a high-potency topical corticosteroid may be helpful. More severe cases usually require the use of oral steroids, usually for two to three weeks, as a shorter course will often be followed by rebound dermatitis. Antibiotics are used only if there is evidence of secondary infection.

- Dr. Dana Wallace, Vice President, American College of Allergy, Asthma & Immunology (ACAAI)

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