Just about every family seems to include one person who thinks you can go weeks without switching out a bath towel for a clean one. The yin to their yang is the person who says you need a fresh towel for every person, every day. Who's right? Neither, actually.
Why is proper washing important?
Towels get moist when you dry off with them. The porous, damp environment is the perfect breeding ground for bacteria. A common towel can have yeast, mold and E. coli. growing on it, without you ever knowing it. Gross, right? Regular washing prevents bacteria from growing.
Reuse or wash?
There are some variables when it comes to how often you should wash your towels. Consumer Reports says that under normal circumstances, a towel can be used three or four times before it needs to be tossed in the hamper. Now notice, I said "times" not "days." So if you have multiple family members using a towel, then on the third or forth use it needs to be washed. This goes for hand towels, too.
Also, the condition of the person using the towel matters, too. If they're sick, toss it in the laundry after one use. If it's flu season, it's best that every family member have their own towel -- even if they aren't exhibiting symptoms -- to prevent the potential spread of germs.
What temp wash?
The Infection Control Department of Mid-Western Regional Hospital of Ennis, Ireland recommends washing towels in water that is at least 140 degrees Fahrenheit (60 degrees Celsius) or more to kill bacteria. So, if you have a sanitize mode on your washing machine, use it. If not, you may consider raising the temperature on your water heater while washing that load. Be sure young children are supervised around sinks, tubs and showers while you do laundry, though, to prevent burns.