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Stinging hairs, a real health problem

The venomous nature of the oak processionary caterpillar lies in the presence of numerous microscopic stinging hairs (a tenth of a millimetre long) on the caterpillar which are formed from the third larval stage (from May onwards) and form an active defence mechanism for the species.

The stinging hairs are a characteristic arrow shape with barbs. Due to their special shape they can easily penetrate the superficial layers of the skin, the eyes and the upper respiratory tract.

The hairs from the (old or new) cocoon nests can also be blown along by the wind or be released and spread by vibrations from traffic. Clothes contaminated with stinging hairs can also be a source of transmission of these hairs to other people. The hairs of old, dead caterpillars or in old cocoon nests also remain active for a long time (five years). Exposure to the stinging hairs of the caterpillars mainly occurs by inhalation or skin contact and to a lesser degree by direct contact with the caterpillars themselves.

Effects on health

Besides the fact that, due to their special shape, the stinging hairs can easily penetrate the superficial layers of the skin, the eyes and the upper respiratory tract and cause small painful sores there, after penetration they also release a toxin in the form of a foreign protein ‘thaumetopoein’ which causes allergic reactions. Experience with patients shows that reactions can be much stronger in the case of repeated contact or sustained exposure (for example from clothing), It is also clear that reactions resulting from contact with the stinging hairs can vary greatly from person to person.

Effects on the skin

Localised symptoms, resulting from severe irritation and inflammation, may occur within eight hours after contact with the stinging hairs. A painful red rash appears with severe itching. The appearance of the skin may vary considerably: from bumps and pimples to fluid-filled blisters, which may become inflamed. This can occur not only on exposed skin, but also on other parts of the body. The hairs can easily spread to other parts of the body by perspiration, scratching and/or rubbing. Long-term contact with the skin can also occur due to the presence of hairs in clothing.

If left untreated the symptoms disappear within two weeks, provided that no further contact occurs. In that case, reactions can be far more severe.

Effects on the eyes

If stinging hairs enter the eyes, they can cause severe painful reactions, redness and itching, with inflammation in some cases, within one to four hours. Symptoms will continue as long as stinging hairs remain there.

Effects on the upper respiratory tract

Following inhalation, the stinging hairs can also cause irritation or inflammation of the mucous membrane of the upper respiratory tract (nose, throat and major airways). Initially, the symptoms are similar to a head cold. People may also complain of a sore throat and possibly problems swallowing. Shortness of breath may sometimes occur.

General symptoms

Besides localised symptoms, general symptoms may also occur: fever, general unwellness, dizziness and vomiting.

Possible treatments

Symptoms generally disappear within a few days or weeks. Partly to prevent the stinging hairs from spreading further over the body and inflammatory reactions from progressing, it is important to wash the skin thoroughly with water and rinse affected eyes thoroughly with water. In the early stages, adhesive tape may be applied to the affected skin to remove superfluous hairs quickly (painful for men). As it is difficult to remove hairs from clothes, it is also recommended that they be washed very thoroughly with soap and water, particularly when the person knows that he or she has been in an infested area and has been troubled by the stinging hairs.

Supporting drug therapy is not necessary for slight symptoms. Soothing products containing camphor or menthol can provide relief from severe itching. For stronger treatment the GP should be consulted.

More information

For further details on health aspects, visit the Medical Environmental Experts at LOGO’s website.