Many people have a bottle of hand sanitizer in their car, on their desk, or in their home. We use it to clean our hands and kill the germs that could get us sick. But, what many don't know is that they might not want their hands to be too clean.At Hilltop Middle School, pumping hand sanitizer to wipe clean and stay healthy is a regular exercise for students.Jennifer Heinz, who works at the school, said, "The kids know where [the bottles of sanitizer] are at: locker rooms, office areas, they're posted at different areas on campus."In fact, they sanitize everything from countertops to windows -- anything to kill the bacteria that could lead to a cold, or worse: the swine flu. They're not alone. Hand sanitizer sales have gone up more than 70 percent this year. The 10News newsroom is a perfect example. Almost every desk has a pump guaranteeing to kill 99.99% of germs. But hold on a second. New research out of UCSD says you may not want to kill all of those germs."That's right," UCSD's Richard Gallo, M.D. Ph.d. said. "It looks like there's a pro and con."The con is that we need some of those germs -- also known as bacteria -- living on our skin. While some bacteria get us sick, researchers found a germ that actually protects our immune system."When it's absent, if there's any kind of injury to the skin you get excessive inflammation from that," Gallo said.Dr. Gallo said stripping our hands of all bacteria also strips us of some of our natural defenses against other infections. "If you have no bacteria of this sort, that's bad," he said.But Dr. Gallo said you still need to kill the bad germs. Right now, he just doesn't know how much hand sanitizer is too much or how much bacteria we need on our skin. That's for the next study.