Homes are designed to keep heat inside during the winter. In addition, most people make an extra effort to seal out the cold by adding extra insulation and filling any cracks that may cause drafts. By doing this, they are also sealing out fresh air. This lack of fresh air increases the concentration of both allergens and pollutants in the home and lowers the indoor air quality. According to the EPA, poor winter indoor air quality can contribute to respiratory conditions such as asthma.