Teddy in the Freezer: How Much Cold Can Mites Tolerate?

Soft toys are delicate. Most of them can’t be washed at high temperatures without losing their shape. Parents of children with house dust mite allergies are therefore advised to put soft toys in the freezer on a regular basis. The cold temperature kills the mites and the allergens can then be rinsed out at a low temperature. But how long should soft toys be left in the cold? There was previously no research on how much time it takes for mites to freeze and stop laying eggs.

Scientists at Wright State University in Ohio investigated the matter. They kept female mites of the species Dermatophagoides farinae at temperatures of – 4, -12 and -15 degrees Celsius. The ones in the control group were exposed to a temperature of 23 degrees Celsius and 75 per cent humidity – an optimal climate for mites. The researchers took the mites out from the cold at several points over the course of two days and then observed them for two weeks at room temperature. The mites initially appeared to be insensitive to the cold. More than half of the arachnids survived for six days after 24 hours in the freezer (-15 degrees Celsius). By the 15th day, however, all the mites died without having laid any eggs. Nearly all the mites in the control group survived and laid eggs.

  • The biologists concluded that, to rid soft toys of house dust mites, they need to be kept in the freezer for two days at -15 degrees Celsius and then rinsed. The researchers believe that this finding may apply to other mite species, such as Dermatophagoides pteronyssinus, which can also cause problems for allergy sufferers.