Allison's grandmother was shocked to see the 5-year-old going off to kindergarten with freshly washed wet hair. "That's why she gets so many colds," Grandma said. Allison has had her share of colds. But Grandma's wet-hair theory is all wet. Wet hair, cold weather or drafty rooms do not directly cause colds, but such conditions can make the body more susceptible to catching them.