May 21, 2007 -- Hotter is better when it comes to killing dust mites and other allergens in your laundry.

A new study shows washing laundry in hot water (140 degrees Fahrenheit) kills 100% of dust mites. But turn the dial down just 36 degrees to a warm, 104 degree Fahrenheit wash and only 6.5% of dust mites are killed in the laundry. Hotter water was also better at removing dog dander and pollen.

But if your delicate laundry can’t take the heat, researchers also suggest another way to reduce dust mites and allergens in the laundry: wash at a lower temperature (between 86-104 degrees Fahrenheit) and then rinse the laundry twice with cold water for at least three minutes each.

In the study, presented at the American Thoracic Society’s 103rd International Conference in San Francisco, researchers compared the effectiveness of washing cotton sheets with regular laundry detergent at various temperatures in removing dust mites, dog dander, and pollen allergens.

The results showed that washing laundry at hotter temperatures was significantly more effective than warm water at killing dust mites as well as other allergens. For example:

• Washing laundry in warm, 86- to 104-degree Fahrenheit water killed only about 6% of dust mites.
• Hot water washing (at 140 degrees Fahrenheit) killed 100% of dust mites.
• Washing in hot water also removed nearly 90% of dog dander compared with about 60% removed in warm water washing.
• Hot water washing removed nearly 97% of pollen in the laundry compared with 69% at 86 degrees Fahrenheit and 95% at 104 degrees Fahrenheit.
• The study also showed that steam cleaning of the sheets was equally effective as hot water (140 degrees Fahrenheit) washing at killing dust mites and removing dog dander and pollen.

In addition, researcher Jung-Won Park, MD, PhD, of Yonsei University in Seoul, South Korea, and colleagues found rinsing laundry twice in cold water was also effective at removing all traces of dog dander in laundry washed at any temperatures.