What should you know about oral antihistamines for allergic conjunctivitis?

Allergic conjunctivitis happens when the surface of the eye reacts to an allergen, causing itching, redness, watering or stringy discharge. An oral antihistamine blocks histamine, one of the chemicals involved in the reaction. It may be useful when eye symptoms occur alongside nasal allergy symptoms such as sneezing or a runny nose. Some products can cause sleepiness, dry mouth or blurred vision, so check the label and mention other medicines or health conditions to a pharmacist or clinician.

Use the product exactly as directed and do not combine antihistamines unless a clinician or pharmacist advises it. Avoid rubbing your eyes; a cool clean compress can soothe irritation. Wash hands after outdoor exposure, keep windows closed when triggers are high, and consider prescribed antihistamine or mast-cell stabilising eye drops when symptoms are mainly ocular. Contact-lens wearers should remove lenses during active irritation and ask when it is safe to replace them. Allergy testing may help when the trigger is unclear or symptoms keep returning.

Seek urgent assessment for severe eye pain, marked light sensitivity, sudden vision change, an injury, or swelling that makes it difficult to open the eye. Arrange medical review for one-sided symptoms, thick discharge, symptoms that do not settle, or repeated episodes without an obvious trigger. These features can have causes other than allergy and may need a different treatment.

Ask which medicine suits your age, pregnancy status and other treatments; whether an eye drop would target the problem better; how to manage contact lenses; and whether allergy testing is appropriate.