Dryer heat is not enough to kill all germs.

More Info: In an interesting study presented at the American Society of Microbiologists meeting, Dr. Chuck Gerber from the University of Arizona tested washing machines and dryers to answer this very question.  What he found was that washing in warm water did not kill many of the germs present prior to washing, and that in fact, it left germs behind in the washing machine even after the wash was transferred to the dryer.  Though the dryer did manage to kill some of the germs, it was not effective in killing the vast majority.

How to Kill Germs in the Laundry

It is possible to kill germs in the laundry. First, washing clothes in a hot water cycle may kill certain species of bacteria that are simply unable to survive at high temperatures. Chlorine bleach containing at least 5.25% sodium hypochlorite will effectively kill most germs in the washing machine in hot water.  Though the exact properties are not wholly known, vinegar does have antimicrobial properties. One cup of vinegar added to the laundry can break down soapy residue and uric acid, dissolve the alkalies and soaps in detergents for a cleaner rinse, removing wine and deodorant stains, and keep colors from fading. 

How to Prevent Germs in the Laundry

The first step to prevent germs in the laundry is to presoak any clothes that are soiled with bodily fluids, such as blood or urine. During the presoaking process, use the cold or warm water cycle, as hot water can cause the stains to set in fabrics. When washing the laundry, put the water cycle on the hottest setting. Wash underwear, towels and other linens with a bleach product to prevent the spread of germs. Thoroughly dry the laundry in a dryer using the highest heat setting to rid the items of any possible remaining germs. To prevent germs from multiplying overnight, never leave wet laundry inside the washing machine.