Even if you spend a lot of your time outdoors during the summer months, remember that to feel good you have to breathe in pure air indoors.
Any location operating in isolation will generate numerous pollutants that are harmful to the body. Cigarette smoke, air conditioning and bacteria, etc. are important sources of allergies.
Therefore, even if clean, any accommodation or second home that has not been used in a while will remain a primary source of pollutants.