Allergic reactions are caused by sensitivity to an allergen. Most often allergic reactions, for instance runny nose or eye symptoms, are triggered by pollens, animal dandruff, flour or chemicals. You can relieve the symptoms with over-the-counter medication.
Allergic reactions are usually triggered by adequate exposure to the allergen. You can have allergic rhinitis-like symptoms also without an allergy (non-allergic hypersensitivity rhinitis). Hypersensitivity rhinitis symptoms may also be induced by exercise.