Antihistamines for bug bites

An oral antihistamine is the sensible choice when there are several bites, when they are somewhere a cream cannot easily go, or when the itch is keeping you awake. A non-drowsy tablet such as cetirizine, loratadine or fexofenadine once a day suits the daytime; a sedating one such as diphenhydramine is sometimes used at night for that reason alone. Antihistamine creams are widely sold and best avoided.

Why they help at all

Much of a bite's itch and the raised wheal around it are driven by histamine released by mast cells in the skin. Antihistamines block the receptor histamine acts on, so the itch and the swelling are damped. This is also why they work better for some bites than others: a mosquito bite is largely a histamine story, whereas the immediate pain of a wasp sting is not, and no antihistamine will touch it.

Which one

Follow the dose on the package for your age and weight, and check with a pharmacist before combining an antihistamine with other medicines — sedating ones in particular add to the effect of anything else that causes drowsiness, including alcohol.

First-generation antihistamines deserve more caution in older adults, where they are linked with confusion and falls, and in young children, where paradoxical agitation is common. If the only reason for choosing one is to sleep through the itch, treating the bite itself — cold, hydrocortisone 1%, covering it so scratching is harder — is often the better trade.

Where antihistamines do not help

• The pain of a sting. Wasp, hornet and bee stings hurt because of venom, not histamine alone. Cold and a simple painkiller do more in the first hours.
• Infection. Antihistamines do nothing to bacteria. Spreading warmth, increasing pain after day two or three, pus, a red streak or fever means a clinician, not a stronger tablet.
• A severe allergic reaction. This is the one that matters. Swelling of the lips, face, tongue or throat, difficulty breathing, wheeze, dizziness or collapse after a sting is anaphylaxis, and an antihistamine is not the treatment for it — adrenaline (epinephrine) is, followed by emergency care. Anyone who has had such a reaction should be carrying an auto-injector and using it rather than reaching for a tablet.

Practical combinations

For a handful of ordinary itchy bites: cold pack now, hydrocortisone 1% on the marks, a non-drowsy antihistamine once a day while the itch lasts, and nails kept short. For dozens of bites over a large area, or bites in places you cannot reach, the tablet does the work the cream cannot.

If the itch has not started to settle after several days on that combination, the question is no longer which antihistamine. It is whether this is a bite at all — scabies, an allergic rash or a skin condition can all look like bites and none of them respond to this approach.