Pollens tend to be very seasonal so it could be a specific type of pollen outside, or it could be due to an inadequately ventilated or insulated (and very hot)

Pollens tend to be very seasonal so it could be a specific type of pollen outside, or it could be due to an inadequately ventilated or insulated (and very hot) attic pushing stuff into the rest of the house during the summer months. If you have lived in the same town for over five years without any issues then it probably is not pollen. In which case if you own the house then you can have someone check the attic ventilation, and schedule the hvac system to be cleaned out or replaced. If you rent then just plan on moving within a year.