Mouse allergens can cause major problems for people who live in rodent-infested houses, which - admit it - is an awful lot of us. Mouse dander and urine can set off asthma attacks. In this study, researchers with the National Institute of Environmental Health Sciences looked at what proportion of houses have a protein that comes from mouse urine.

What the researchers wanted to know: Just how widespread is mouse pee?

What they did: In 1998 and 1999, intrepid samplers armed with vacuum cleaners went to 831 homes in 75 locations across the country and sucked up dust to be analyzed for a whole range of allergens. The homes were sampled carefully to represent U.S. homes in general. An adult in each home also filled out a questionnaire.

What they found: An estimated 82 percent of U.S. homes had a mouse urinary protein in at least one location. Kitchen floors were most likely to have the proteins, and high-rise apartments, mobile homes, duplexes, and triplexes had higher concentrations. All but 5 percent of inner-city homes had mouse allergens. Mouse allergens were more common in lower-income households, but half of homes with a household income over $60,000 had the allergens, too.

What the study means to you: Chances are good that you have mouse allergens in your house.

Find out more: Allergy-proof your house: www.medicinenet.com

A humane way to catch a mouse: www.kolias.com/homegarden/mouse.htm

Mice can have allergies, too: http://koti.mbnet.fi

Read the article: Cohn, R.D., Arbes, S.J., Yin, M., Jaramillo, R., and D.C. Zeldin. "National Prevalence and Exposure Risk for Mouse Allergen in U.S. Households." Journal of Allergy and Clinical Immunology. June 2004, Vol. 113, No. 6, pp. 1167-1171.

Abstract online: www.ncbi.nlm.nih.gov