Insect bites and stings

Ordinary insect bites and stings are an itch and a swelling problem, with one exception that is a life-threatening emergency.

Itch control, in order. A cold pack; an oral antihistamine (a second-generation one in the daytime, a sedating one at night); a topical corticosteroid for a large local reaction; and calamine or a plain moisturiser. Do not scratch — scratching breaks the skin and secondary bacterial infection is the main complication of a bite.

Plantain and other demulcent, astringent leaves are the traditional bite remedy and are harmless: a crushed leaf held on the bite, or a cooled infusion on a cloth. The evidence is modest and the harm is nil.

Bee and wasp stings. Scrape the sting out sideways with a fingernail or card (do not squeeze the venom sac), cool the area, and use an antihistamine. A large local reaction — swelling spreading well beyond the sting over 24-48 hours — is uncomfortable and usually not dangerous; it is different from anaphylaxis.

Anaphylaxis is the emergency and it is not a plant problem. Widespread hives, swelling of the lips, tongue or throat, difficulty breathing, wheezing, a feeling of impending doom, dizziness or collapse, after a sting or a food. The treatment is intramuscular adrenaline (epinephrine) from an auto-injector, given immediately, and then emergency services. Antihistamines do not treat anaphylaxis. Anyone with a known risk should carry two auto-injectors and know how to use them, and anyone who has had a reaction should be assessed by an allergist.

Plant contact reactions. Poison ivy, oak and sumac cause an allergic contact dermatitis, not an immediate reaction. The treatment is washing the skin with soap and water within 30 minutes of exposure (the urushiol must be removed before it binds), then cool compresses and topical steroids. The rash is not contagious — the fluid in the blisters contains no urushiol, and the belief that it spreads is because the eruption appears in stages. Severe cases, especially on the face or genitals, need medical treatment.

The bites that are not ordinary bites. A spreading red area around a bite with fever; a bite with a target-shaped rash (possible Lyme disease); a bite that becomes a black eschar (possible a spider or a venomous bite); and any bite in a person who is immunosuppressed.