Most people can't stay inside all the time, and, in any case, pollen comes inside through open doors and windows and on people's clothes, hair and shoes. Keep all windows closed. Change clothes after coming in from outside, and wash the clothes before wearing them again. Keep dirty clothes out of the allergic person's bedroom. Wash the allergic person's hair every night to avoid transferring pollen from hair to pillow.
Some indoor allergens are also difficult to avoid, but they can be reduced.
Mites like to live in box springs, mattresses, pillows, and carpets. To keep the mite population down, the allergic person's mattress, box spring, and pillows should be encased in special covers available from companies that make allergy-proof products. Washable curtains should be the only window coverings. Carpets should be removed or treated with an anti-allergen spray. For those with allergies to pets, the simple answer, giving up a beloved cat or dog, is often unacceptable.