Allergic conjunctivitis: pollen, itching and what the studies say

The pollen season arrives, and with it an itch in the eyes that gives no respite. The eyes water and turn red, the eyelids swell; sometimes sneezing and a runny nose are added. The temptation to rub them is very strong.

Allergic conjunctivitis is one of the most widespread eye problems: according to a 2013 systematic review it affects up to 40% of the population, but only a small proportion of those who suffer from it see a doctor¹. Many regard it as a nuisance to be put up with. The studies, however, have something to say: on how it is recognised, on how much it really weighs and on what helps.

In this article

1. What happens in an allergic eye
2. Seasonal, perennial and the rarer forms
3. Allergic conjunctivitis: how to recognise it
4. Not just a nuisance: the impact on everyday life
5. Antihistamine and mast cell stabiliser eye drops: what Cochrane says
6. Cold, artificial tears and hands away from the eyes
7. When it is not the usual allergy
8. Frequently asked questions
9. Sources

What happens in an allergic eye

The conjunctiva, the transparent membrane that covers the white of the eye, contains mast cells, cells of the immune system that store histamine and other inflammatory substances. In people who are allergic, contact with an allergen, for example grass pollen, makes the mast cells release histamine. It is histamine that causes the typical signs: itching, redness, watering².

The two main families of eye drops that have been studied are based on this mechanism. Antihistamines block the receptors on which histamine acts; mast cell stabilisers prevent it from being released². Eye allergy, moreover, rarely travels alone: a 2012 report by experts in ophthalmology and allergy notes that it is often accompanied by other allergic manifestations, above all rhinitis⁴.

Seasonal, perennial and the rarer forms

The most common form is seasonal or perennial allergic conjunctivitis². The first appears in the pollen months; the second lasts all year, linked to allergens that are always present. A 2021 review lists other forms triggered by allergens, such as giant papillary conjunctivitis and allergic contact blepharoconjunctivitis, and two forms that do not always depend on a specific allergen: vernal keratoconjunctivitis and atopic keratoconjunctivitis³.

According to the same review, allergic conjunctivitis is on the rise, affects children and adults, appreciably worsens quality of life and, in some cases, can cause damage to vision that is not recovered³.

Allergic conjunctivitis: how to recognise it

The most constant sign is itching¹, and it is also what helps most in distinguishing it from infectious conjunctivitis, described in our article on viral, bacterial or allergic conjunctivitis. The diagnosis is usually based on the history and the signs; allergy tests, on the skin or in the blood, are used when the specific allergen needs to be identified. For some specific forms, the same report recommends teamwork between ophthalmologist and allergist⁴.

Not just a nuisance: the impact on everyday life

A Spanish study compared 201 people with seasonal allergic conjunctivitis and 200 people without, recruited in eye clinics in five cities. Those with the allergy reported a lower quality of life in almost all the areas measured, from pain to mood, and worse scores in several aspects of visual function too: vision in general, distance vision, eye pain, the ability to carry out their activities. They were also more often affected by asthma and other allergies⁵. It is an observational study, with patients largely from private clinics, but it confirms that for many people the pollen season is not just an annoyance.

Antihistamine and mast cell stabiliser eye drops: what Cochrane says

An earlier meta-analysis, from 2004, had reached similar conclusions: both categories work better than a placebo, but the evidence is not enough to prefer one over the other; some limited data suggest that antihistamines act more quickly⁶. A 2022 systematic review of 15 guidelines found that they agree in recommending, for allergic forms, antihistamine eye drops, mast cell stabilisers or dual-action medicines⁷.

Cortisone eye drops also exist², but they are a separate chapter: in vernal keratoconjunctivitis, excessive and prolonged use of corticosteroid eye drops has been associated with glaucoma and cataract¹⁰. For this reason their use should be decided and followed by the ophthalmologist.

Cold, artificial tears and hands away from the eyes

The same guidelines also recommend measures without medicines: artificial tears, cold compresses, avoiding or removing the allergen⁷. A randomised trial put them to the test in the laboratory. Eighteen volunteers allergic to grass pollen were exposed to the pollen in a special chamber and then treated, on different days and in random order, with artificial tears, five minutes of cold compress, both, or nothing. Redness and symptoms fell more quickly with the measures without medicines than with no treatment at all; artificial tears and cold together reduced redness more than the other options without medicines, and cold boosted the effect of an antihistamine eye drop⁸. The limitation is obvious: few people, an hour of observation, an allergy provoked in the laboratory.

Then there is rubbing. A 2020 meta-analysis of 29 studies, with over 7 million people in 15 countries, studied the factors associated with keratoconus, a disease in which the cornea thins and becomes deformed. People who rubbed their eyes had about three times the probability of having keratoconus; allergy was also associated, to a lesser extent⁹. These are observational studies: they show an association, they do not prove that rubbing is the cause. We discuss this in our articles on keratoconus and on rubbing your eyes.

When it is not the usual allergy

Vernal keratoconjunctivitis is a chronic form that affects both eyes, above all in young people. As well as itching, it causes discomfort in light, a white, mucous discharge, watering, a foreign-body sensation and, when it involves the cornea with small ulcers, pain. It is treated with different medicines, from antihistamines to corticosteroids and other immunosuppressant eye drops¹⁰.

Frequently asked questions

How can you tell whether conjunctivitis is allergic?

The most telling sign is itching¹, often together with nose symptoms such as sneezing and a runny nose⁴. The diagnosis is based on the history and the signs; allergy tests are used when the allergen needs to be identified⁴.

Can antihistamine eye drops be used for a long time?

The studies in the Cochrane review lasted from one to eight weeks: there are no data on efficacy and safety in the long term. In the short term no serious undesirable effects were reported². How to use them for long periods is a choice to make with the doctor.

Can allergic conjunctivitis damage vision?

Seasonal and perennial forms weigh above all on quality of life⁵. Some rarer, chronic forms, such as vernal keratoconjunctivitis, can however involve the cornea and, at times, leave permanent damage^3,10.

Do cold compresses really help?

In a small laboratory study, cold compresses and artificial tears reduced redness and symptoms more quickly than no treatment, and cold boosted the effect of an antihistamine eye drop⁸. The guidelines list them among the measures without medicines⁷.

Allergic conjunctivitis is common and can weigh heavily on the days of those who suffer from it. The studies offer few certainties on the long term and many confirmations on the short term: the eye drops studied reduce symptoms, cold helps, and keeping your hands away from your eyes is a habit with good reasons on its side.