What is allergic conjunctivitis?

Allergic conjunctivitis is inflammation of the conjunctiva (the thin clear tissue covering the white of the eye and lining the inside of the eyelids) caused by an allergic reaction. The classic features are itching (often the most prominent feature), redness, watery discharge, eyelid swelling, and a sensation of foreign body in the eye.

The types.

Seasonal allergic conjunctivitis: triggered by seasonal allergens like tree, grass, and weed pollens. Symptoms come and go with the allergen seasons.

Perennial allergic conjunctivitis: triggered by year-round allergens like dust mites, pet dander, and indoor moulds. Symptoms persist throughout the year.

Vernal keratoconjunctivitis (VKC): a more severe form, particularly affecting children and adolescents, often in warmer climates. Can affect the cornea (the clear front of the eye) and threaten vision in severe cases.

Atopic keratoconjunctivitis (AKC): a severe form occurring in adults with atopic dermatitis. Can also affect the cornea and threaten vision.

Giant papillary conjunctivitis: a form often associated with contact lens wear or other foreign bodies.

Why it happens. The conjunctiva contains immune cells that respond to allergens. In allergic individuals, exposure to allergens triggers release of histamine and other inflammatory molecules from these cells, producing the symptoms. The biology overlaps with broader atopic disease (allergic rhinitis, asthma, atopic dermatitis), and people with one atopic condition often have others.

The therapy options.

For mild and moderate allergic conjunctivitis: cool compresses, artificial tears, and allergen avoidance where feasible. Topical eye drops combining antihistamine and mast cell stabiliser (olopatadine, ketotifen, alcaftadine, others) are the workhorse therapy and provide both immediate and ongoing benefit. Oral antihistamines can help, particularly when there are also nasal symptoms.

For more persistent or severe disease: topical NSAIDs, short courses of topical low-potency corticosteroids for flares (used carefully because of eye-related corticosteroid risks), topical immunomodulators (cyclosporine, tacrolimus off-label) for chronic disease.

For severe disease (VKC, AKC) with corneal involvement: dedicated specialty care, often with topical immunomodulators, careful corticosteroid use, and consideration of systemic immunosuppression. Biologic therapy with dupilumab (off-label) is an option for some patients with severe ocular allergy associated with broader atopic disease, given the shared underlying biology.

What to expect. For most people with seasonal or perennial allergic conjunctivitis, modern combined topical therapy controls symptoms well. For those with more severe forms, specialty ophthalmology (and often allergy-immunology) care is the right setting. The overlap with broader atopic disease means that addressing the whole picture (with a clinician who can think across organ systems) often produces better outcomes than treating the eye in isolation.