If you have a newer, more airtight house, the indoor air may only be exchanged with outdoor air every few hours. Older homes, on the other hand, have more frequent air exchanges because they do not have vapor barriers or as much insulation. If you have an energy-efficient home consider buying an air exchanger. This will change the air in the house more frequently and help to reduce indoor pollution. Also, open your windows in the warmer months to provide better ventilation, particularly in a basement. Be aware, however, that outdoor pollutants can also cause problems so make sure that you are not allergic to them, or you will simply be replacing one allergen with another.