The biggest problem on beds is dust mites. They live off of dead human and pet skin and thrive in the humid conditions created by the moisture we give off while we sleep. Mites defecate as often as 20 times a day, according to Tim Lockley, a entomology expert and former U.S. Agriculture Department scientist. About five percent of the population is allergic to these droppings. It is recommended that those who suffer such allergies clean their sheets daily, vacuum their mattress several times a week and cover their pillows with a special protective cover designed to keep mites out.

On the Other: Once a Week is Considered the Standard

Most cleaning services recommend changing your sheets and pillowcases about once a week. Other bedding such as duvet covers should be washed monthly. To control dust mite problems in between washings, Lockley recommends you wait until after noon to make the bed. Making the bed keeps the humidity level high on the sheets, which mites like. Leaving the bed exposed to the open air reduces moisture. "Mites don't like it if the humidity falls below 50 percent," Lockley writes.

Bottom Line

Changing the sheets and pillowcases about once a week is fine for most people. For those with special conditions, like mite allergies, washing the sheets every day or every couple days may be necessary.

Source:

Real Simple: How to Best Wash Your Sheets

Sun Herald: Dust Mites are a Part of Everyday Life