Allergic Conjunctivitis

Allergic conjunctivitis is a bilateral conjunctival reaction to an environmental or contact allergen, and one of the most common causes of a red, irritated eye.^[1] Itching is the dominant symptom — if a patient with a red eye does not report itching, seriously reconsider allergic conjunctivitis as the cause. The essential first task is not treating the itch — it is confirming this is conjunctivitis and not a sight-threatening red-eye mimic (angle-closure glaucoma, iritis/uveitis, scleritis, keratitis), and recognizing when allergic eye disease is severe enough (vernal or atopic keratoconjunctivitis) to threaten the cornea and need specialist-directed therapy.^[2]

Typical (seasonal/perennial) allergic conjunctivitis

Bilateral, itch-predominant, watery/stringy mucoid discharge, chemosis (conjunctival swelling), and lid edema. Often seasonal (pollen) or perennial (dust mite, pet dander), or triggered by a known contact allergen or contact lens wear (giant papillary conjunctivitis). Usually a history of atopy, other allergies, or asthma/eczema.

• History of atopy — asthma, eczema, allergic rhinitis, or other known allergies.
• Seasonal pollen exposure, or perennial exposure to dust mite/pet dander/mould.
• Contact lens wear (giant papillary conjunctivitis) or known contact allergen exposure (cosmetics, preservatives in eye drops).
• Personal history of atopic dermatitis (risk factor for atopic keratoconjunctivitis specifically).
• Male sex, younger age, and warmer climate (risk factors for vernal keratoconjunctivitis specifically).

Differentiating bacterial, viral, and allergic conjunctivitis, and blepharitis

These four conditions are the most commonly confused causes of a red, irritated eye in community practice. Distinguishing them correctly determines whether the patient needs an antibiotic, supportive care, an antihistamine, or eyelid hygiene — and getting it wrong means either an unnecessary antibiotic or a missed diagnosis.

Bacterial conjunctivitis — purulent discharge with morning crusting. (CNX OpenStax, CC BY 4.0, Wikimedia Commons)

Viral conjunctivitis — marked redness, watery discharge, often with a preauricular node. (Joyhill09, CC BY-SA 3.0, Wikimedia Commons)

Allergic conjunctivitis — itching is the dominant symptom, often with chemosis (conjunctival swelling). (James Heilman, MD, CC BY-SA 4.0, Wikimedia Commons)

Blepharitis — crusting and scale at the lash base; this is an eyelid problem, not a conjunctival infection, though it can cause secondary conjunctivitis. (Imrankabirhossain, CC BY-SA 4.0, Wikimedia Commons)

History

• Itching versus pain/photophobia — itching should dominate the history in true allergic conjunctivitis.
• Seasonal pattern, known triggers, or contact lens wear.
• Personal or family history of atopy — asthma, eczema, allergic rhinitis.
• Any thick, ropy discharge or photophobia, which raises concern for vernal/atopic keratoconjunctivitis rather than typical seasonal disease.

Examination

• Best corrected visual acuity.
• Inspect for chemosis, lid edema, and papillary reaction; evert the upper lid to look for giant papillae if vernal keratoconjunctivitis is suspected.
• Fluorescein staining if corneal involvement (shield ulcer) is possible.
• Bilateral findings support allergic conjunctivitis — unilateral redness should prompt reconsideration of the diagnosis.

• Control itching and inflammation.
• Identify and reduce allergen exposure.
• Prevent corneal complications in severe (vernal/atopic) disease.
• Provide symptomatic relief.

• Identify and avoid/reduce the specific allergen where possible — pollen, dust mite, pet dander, a specific cosmetic or contact lens solution.
• Cold compresses for symptomatic relief.
• Stop wearing contact lenses during a flare; consider a different lens type or care solution if giant papillary conjunctivitis related to lens wear is suspected.
• Avoid eye rubbing — worsens mast-cell degranulation and can contribute to mechanical corneal irritation.
• Preservative-free artificial tears can help dilute and flush allergen from the ocular surface.

Pregnancy/breastfeeding

Topical ophthalmic antihistamines/mast-cell stabilizers have minimal systemic absorption. Discuss any topical corticosteroid or immunomodulator use with the prescriber managing the pregnancy.

Children

Vernal keratoconjunctivitis predominantly affects children and young adults and needs ophthalmology co-management given the corneal risk — do not manage as simple seasonal allergic conjunctivitis.

Contact lens wearers

Giant papillary conjunctivitis related to lens wear or lens-care solution needs the trigger identified and modified (different lens material, care system, or wear schedule), not just symptomatic antihistamine treatment alone.

Reassess if symptoms do not improve within 1-2 weeks of allergen avoidance plus topical therapy. Seasonal disease should improve as allergen exposure declines; perennial or unusually severe/persistent disease warrants reconsidering vernal or atopic keratoconjunctivitis and referring for specialist assessment.

1. Reconfirm the diagnosis and specifically re-examine for giant papillae or corneal involvement suggesting vernal/atopic keratoconjunctivitis rather than assuming simple treatment failure.
2. Reassess for an unidentified or ongoing allergen exposure, including contact lens solutions and cosmetics.
3. Escalate to a specialist-directed topical corticosteroid or immunomodulator (cyclosporine, lifitegrast) for confirmed severe/chronic disease.
4. Refer to ophthalmology for any corneal involvement, or disease not responding to standard topical antihistamine/mast-cell-stabilizer therapy.

• Prescribing a topical antibiotic for allergic conjunctivitis — does not treat an allergic reaction and delays correct management.
• Missing vernal or atopic keratoconjunctivitis by treating a child or atopic adult with severe, chronic disease the same as typical seasonal allergic conjunctivitis.
• Using an ophthalmic corticosteroid for routine allergic conjunctivitis without specialist supervision — real efficacy, but long-term risk of glaucoma/cataracts requires monitoring.
• Overusing ophthalmic vasoconstrictors/decongestants for allergic redness — causes rebound hyperemia and tachyphylaxis; limit to occasional, short-term use.^[4]
• Not asking specifically about itching — the single most useful symptom for distinguishing allergic from bacterial/viral conjunctivitis.

How to use this table: Doses are adult doses and require patient-specific confirmation (renal/hepatic function, weight, allergy history). Pediatric dosing is weight-based per the current product monograph unless stated. Drug pricing is intentionally omitted. Select any drug name to open its complete Pharmasist Drug Database page.

Ophthalmic antihistamines and mast-cell stabilizers

1st line for typical seasonal/perennial allergic conjunctivitis.

Ophthalmic NSAIDs

Ketorolac has specific labelling for seasonal allergic conjunctivitis itching in some formulations.

Ophthalmic corticosteroids

For flares of vernal/atopic keratoconjunctivitis, specialist-directed only, short-term (typically ≤2 weeks) with monitoring — long-term use raises glaucoma/cataract risk.

Ophthalmic immunomodulators

For chronic control of vernal/atopic keratoconjunctivitis — specialist-directed; full response may take weeks to months.