Dendrolimus dermatitis is an acute dermatitis caused by contact with the poisonous hairs of Dendrolimus.


The pathogen is Dendrolimus, also known as pine caterpillars.

The larvae, molts, and cocoons of pine caterpillars are with large amounts of poisonous hairs, which can cause the disease. In addition, exposures to the weeds, fertilizers or water contaminated by poisonous hairs may cause the disease.

Signs and Symptoms

The main manifestations are dermatitis, arthritis, bumps, otitis, and ophthalmitis.

After contacts with poisonous hairs, severe localized pruritus occurs within few minutes. Subsequently, there are bright red, edematous maculopapular rash or wheals, and sometimes vesicles may occur. The skin lesions are mostly on the neck, shoulders, chest, back, and flexor surface of the extremities. After treatment, the skin lesions heal in 3 - 7 days.

Generally, arthritis can occur 1 - 2 days after eruption, mostly in the metatarsals, fingers, knees, wrists, elbows, and ankles, usually unilateral, and there are only 1 - 2 joints involved. The affected joints have obvious swelling and pain, and their function is limited. Generally, the symptoms subside 1 - 2 weeks, but may persist for several months in some patients. Recurrent attacks may result in joint deformities in few patients. There is low-grade fever in severe patients.

Bump occurs mostly on the exposed areas such as extremities, hands, and feet. There is mostly single, gradually enlarged, softened, and undulated bump. There is bloody exudate or pus in the bump, and the bump subsides spontaneously after rupture, persisting for 1 - 2 months.

Otitis and ophthalmia may occur in few patients. After treatment, collapse of the auricle may be present. Iridocyclitis and scleritis may occur and cause blindness in severe patients.


If there are a history of exposure to pine caterpillars and clinical manifestations, the disease can be diagnosed.


Topical calamine lotion can be used.

Arthritis can be treated with non-steroidal anti-inflammatory drugs as appropriate. Acute joint pain can be treated with indomethacin 25mg 3 times a day, and oral corticosteroids or local block treatment can be considered if necessary. Functional exercises are required after arthritis is relieved to prevent from malformation.