Hayfever often involves the eyes just as much as the nose, and it is the eye symptoms that can help to distinguish it from the common cold, and to some extent from allergies to other airborne substances such as mould spores and house dust. Given the way air flows around the body, particles of different sizes and shapes move around us in different ways, and settle out of the air at different points on the body's surface. The size of pollen grains makes them especially likely to flow close to the eye as we walk or run about, and to stick to its moist surface.

When the eyes react allergically to pollen, they first tend to water copiously. In the normal, healthy eye, tear fluid is secreted all the time and flows across the surface of the eye, then drains away down a tiny tube, called the tear duct, that leads from the inner corner of the eye to the nose. In doing so, it sweeps away dust and bacteria, keeping the eye clean and disease-free. The reaction to pollen during the hayfever season is simply an exaggerated version of this normal cleansing process.

One of the consequences of a blocked nose, or a nose that is producing a great deal of watery mucus, is that the tear duct runs into a dead end, or an already flooded channel. Either way, the tear fluid cannot seep away, so an overflow occurs at the top of the tear duct. Since there may well be more tears from the eye anyway, the overflow can become a steady stream of tears down the face. The effect is similar to a heavy storm on a house whose drainpipes are already choked with leaves.

Watery eyes, however, are only a minor symptom. In some people there is also conjunctivitis, inflammation of the outer surface of the eyeball, the conjunctiva. The effect is to produce soreness, redness and severe itching of the eyes. Occasionally conjunctivitis (pink eye). is the only sign of hayfever with no symptoms in the nose at all.

Anyone who wears contact lenses and also suffers from hayfever is likely to find the lenses especially uncomfortable during the pollen season. Some people have to revert to glasses for a few weeks at the height of the season. However, certain types of lens, or certain cleaning solutions, may be aggravating the sore eyes, and a change may make it possible to keep wearing lenses all year round. A good optician should be able to advise you on this point. Bear in mind that glasses can help to keep pollen out of the eyes , so abandoning lenses for a while may have a double benefit.

Some people are unfortunate enough to suffer far more serious eye problems, ranging from swollen eyelids to very severe inflammation in the eye that can lead to blistering or ulceration. Needless to say, severe inflammation requires prompt medical treatment as there is a risk of blindness.