The latter is what people mean when they say 'hay fever'. Seasonal rhinitis is usually caused by pollen from plants which come into season in summer and early spring, or sometimes by spores from seasonal moulds, more likely during autumn months. Different types of plants release their pollen in different months, so the months when symptoms are worst can give clues as to what sort of plant is responsible. Mould spores and pollen are by no means the only triggers of rhinitis. House dust mites, pet allergens and all the other airborne allergens can be responsible, particularly for perennial rhinitis because they are in the environment all year round.
Any foods can trigger rhinitis, just as they can asthma.
Some foods may also cause cross-reactions in which people who are allergic to a particular plant's pollen may react to foods made from related plants. For instance, someone allergic to mugwort pollen may also react to camomile tea, made from a plant in the same family. Inflammation causes itchiness and excessive mucus production.