For what length of time do allergy symptoms typically last for?

Allergy symptoms: Allergy is a broad term to describe a variety of symptoms. I suppose what you mean by saying allergy is your seasonal rhino conjunctivitis symptoms or hay fevers. Depending on which aero allergens you are sensitized to, your symptoms will last for that season. Some indoor allergens are found year round like dust mites so you have symptoms all the time.