Caterpillar Rash: Skin Reactions to Urticating Hairs
By Wespenprofis.ch · Reviewed by:Fachbewilligung Schädlingsbekämpfung VFB-S · Updated: 3 July 2026
At a glance
Caterpillar dermatitis is caused by contact with the microscopic urticating hairs of processionary moth and brown-tail moth caterpillars, and shows up as an intensely itchy rash with weals. Change the clothing affected and rinse the skin with plenty of water rather than rubbing it. If you have eye irritation, breathing difficulties or severe allergic symptoms, seek medical advice immediately.
This article is not a substitute for medical advice. If you experience difficulty breathing or swelling around the throat, call 144 immediately.
How caterpillar dermatitis develops
From their third larval stage onwards, processionary moth caterpillars and the caterpillars of the brown-tail moth develop microscopic, hollow urticating hairs containing the stinging toxin thaumetopoein. These hairs break off at the slightest touch and can be carried long distances by the wind. If they penetrate the skin or mucous membranes, they trigger a contact reaction known as caterpillar dermatitis. Direct contact with the caterpillar is not necessary for this; simply being near a nest or standing under an infested tree is enough. Laundry dried outdoors, or objects that have been lying under an affected tree, can also transfer urticating hairs.
Typical symptoms
Within a few hours of contact, intense itching with red weals develops on the areas of skin affected and can last for several days. If urticating hairs get into the eyes, redness, watering and a foreign-body sensation may follow. If they are inhaled, coughing, a scratchy throat and irritation of the airways can occur. The severity of the symptoms varies from person to person and depends on the quantity of hairs taken up as well as on individual sensitivity. Repeated contact over several years can also increase sensitivity, so that later reactions turn out more severe than the first one.
First-aid measures
- Change the clothing affected and wash it separately to avoid further contact.
- Rinse the skin with plenty of water, without rubbing or scratching it.
- Press adhesive tape onto the skin and pull it off again to remove hairs from the surface.
- Do not make the itching worse by scratching, as this drives the hairs deeper into the skin.
- Avoid the area and call in a professional to remove the nest (/prozessionsspinner-bekaempfung).
When you should seek medical advice
If you have eye irritation, breathing difficulties, severe swelling or signs of an allergic reaction, you should see a doctor immediately, especially in the case of children and people with pre-existing respiratory conditions. The urticating hairs also remain toxic in abandoned nests for up to twelve years, which is why professional removal of the nest is important in order to avoid repeated contact. You will find more on identifying the caterpillars responsible in our guide to the oak processionary moth.
Frequently asked questions
What does caterpillar dermatitis feel like?
The typical signs are intense itching and red weals on the skin, which appear within a few hours of contact with the urticating hairs and can last for several days.
What should I do if urticating hairs get onto my skin?
Change the clothing affected, rinse the skin with plenty of water and do not rub it, as rubbing drives further hairs into the skin. Adhesive tape can help to lift hairs off the surface of the skin.
When should I see a doctor?
If you have eye irritation, breathing difficulties, severe swelling or signs of an allergic reaction, seek medical advice immediately, especially in the case of children.