Winter months bring allergen invasion.

From late fall to early spring, more than 40,000,000 Americans wheeze, sneeze, cough, and hack their way through the cold months. It sounds like flu season, but these people, adults and children alike, suffer from something less obvious - indoor allergies. The culprits are allergens, minute particles that cause allergic reactions.

According to the Institute of Medicine of the National Institutes of Health, one out of five Americans will experience an allergy-related illness at some point during their lives, and indoor allergens will be responsible for a significant share of these cases. Moreover, 4,000 people die from allergy-related asthma each year, an increase of 33% over the last decade. Treatment for asthma-related illnesses costs more than $6,000,000,000 a year. Indoor allergens also are linked to childhood asthma, a leading cause of school absenteeism.

As the weather gets colder, people tend to spend more time indoors with windows sealed shut, notes the American Academy of Allergy and Immunology."This decreases air circulation and increases the buildup of indoor allergens such as particles from dust mites, cockroaches, rodents, and certain chemicals, as well as mold spores and animal dander, which is dead skin and dried saliva of pets," explains Alan J. Goodman, an allergist in private practice in New York and New Jersey.

Americans spend more than 90% of their time inside, particularly in winter. If they commute by car, the time spent indoors reaches almost 24 hours straight. Scientists theorize that one of the possible reasons for the steady rise in childhood asthma since the 1970s may be the increase in energy-efficient buildings, which allow little exchange of outside air. Coupled with the increased amount of time spent indoors, this causes an increase in exposure to indoor allergens.

Dust mites are the biggest...