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Ask The Expert

Q: Why do allergies give me itchy, watery eyes? And what can I safely do to alleviate the symptoms?

A: There’s no doubt about it – allergies that affect the eyes can be really uncomfortable. And for some people, they can diminish quality of life quite drastically.

Allergies are the result of a hypersensitive immune system. Normally our immune system fights off threats such as a disease or infection. In someone with allergies, the immune system incorrectly identifies a harmless substance (called an allergen) as a threat. The immune system’s reaction itself creates problems – which often affect our eyes.

Types of Allergies

    There are three kinds of allergies that affect the eyes:
  • Allergies from things we breathe in the air – such as dust, mould, pollen and pet hair.
  • Foreign body allergies. For example, some people with contact lenses may develop allergies to the tear film proteins that build up on the surface of the lenses or to components of contact lens solutions.
  • Atopic dermatitis. A disease (a type of eczema) that promotes allergy conditions in the skin, but can affect the eyes as well.

People who have food allergies (shellfish, etc.) or injection allergies (insect stings or penicillin) do not have symptoms that affect the eyes.

What is Happening


When an allergen affects us, it binds to receptor cells called mast cells. Mast cells exist throughout our bodies, but we have 50 million of them in a mucous membrane on the surface of our eyelids called the conjunctiva.

When mast cells in the conjunctiva come into contact with an allergen, they release a chemical called histamine, which stimulates the nerves in the eye, making it itchy and watery. The eye is trying to remove the allergen, not realizing that it is harmless.

The release of histamine also causes dilation of the blood vessels on the surface of the eye, which makes your eyes red. Other allergy symptoms include trouble with concentration, or difficulty seeing, usually from blurry vision. (If you are in doubt about what is causing any visual symptoms you may have, see your eye doctor. It’s best to know for sure that they are caused by allergies and not something more serious.)

Symptoms will last for as long as you are exposed to the allergen – which in the case of a seasonal allergy, such as ragweed, could be as long as six weeks.

What You Can Do

The first step is to avoid whatever you are allergic to. So if you are allergic to animals, you may want to keep your neighbour’s pal Fido at bay.

Seasonal allergies are pretty tough to avoid – very few ragweed sufferers can move to a colder climate for six weeks come August! In cases like these, treatment is definitely in order.

Typically, allergies in the eye are treated with drops designed to stabilize mast cells or inactivate histamine – and some drops do both. Unlike allergy medications in pill form, eye drops have two advantages that come from being administered topically. They won’t make you drowsy, and in addition, you can safely achieve very high concentrations of the drug in the eye.

Commercial Eye Drops

If your symptoms are mild to moderate, start with drops available without a prescription at any drug store. Be sure to take them according to directions – usually you can safely take the drops two to four times a day.

Make sure you don’t buy drops containing a “vasoconstrictor” – many of them do, but this should be listed on the bottle. These drops constrict blood vessels to make your eye whiter. Over time you can get a rebound effect when you stop taking the drops, where your eyes will be redder than usual. You can also increase your chances of developing glaucoma, particularly if you are at risk for angle closure glaucoma.

Persistent Symptoms

If your symptoms are extremely uncomfortable, you will find that over-the-counter drops aren’t good enough. In that case, visit your eye doctor, who will be able to provide you will a prescription for drops that are much stronger and more effective.

And before you know it, that itching and watering will be gone – and everything will look a whole lot brighter.

The Expert:

Dr. Marino Discepola is an Assistant Professor at the McGill University Health Centre’s Department of Ophthalmology and is on staff at both St. Mary’s Hospital and the Royal Victoria Hospital in Montreal. For the past decade, he has been involved in numerous research projects about medications that treat allergies and the eyes.