If you're doing a lot of hand-shaking, you better carry around the Purell. Because a new study shows most people don't know the correct way to wash their hands.

A new study shows that following a trip to the bathroom, 95% of people don't wash their hands long enough to actually eliminate bacteria.

Some commit even worse hygiene sins: a third don't use soap, and a tenth don't wash their hands at all.

According to the study by Michigan State researchers, men are less hygienic than women. Just half of guys used soap, and 15% didn't wash their hands at all. Among the women studied, 78% of women used soap, and 7% don't wash their hands at all.

So how SHOULD you wash your hands? According to the CDC, you've gotta scrub with warm water and soap for at least 20 seconds. The average person spends only six seconds washing their hands.) Some say to sing the Happy Birthday Song two or three times through when you're at the sink and don't stop scrubbing 'til you're done singing.

You should also, once you're lathered up, scrape your nails down your palm to get the soap under your nails where so many germs live. Then, use a paper towel after you rinse...it's the best way to wipe off any lingering bacteria. (And don't rub your hands together under a dryer...all that does is spread the remaining bacteria.)

And make sure to use a clean paper towel on the door handle to leave the bathroom.

Oh, and the study shows that if the public restroom sink is clean, people are likely to wash longer than in a dirty bathroom.