Seasonal allergic rhinitis is experienced only at certain times of the year. It is due to allergy to pollen and spores. Pollen is released into the air at certain times of the year by plants of many kinds such as trees, grasses, weeds and flowers, while spores are released by fungi such as mushrooms and moulds like those in compost heaps or damp places.

The most frequent cause of seasonal allergic rhinitis is grass pollen, including crops.

Although one may be enough to trigger symptoms, some people's symptoms can be triggered by more than one type of pollen or spore.

Because different pollens and spores are released throughout the year to help identify those that cause allergy it may help to note when and where symptoms occur. Pollen is usually released on hot still or windy days, or just after light rain.