It’s one of the first things mothers teach children: Wash your hands with soap and water. But experts, like Mom, say most of us are not doing it right.

Believe it or not, poor hand-washing habits are a big problem, especially in hospitals, where doctors and nurses fail to wash their hands properly half the time.

When kids and adults spread germs, you might think the worst thing is that someone may catch a cold. Wrong. Germs spread by people’s hands cause diarrheal problems, pneumonia and other deadly infections, especially in communities where clean water and soap are in short supply.

Proper hand-washing is “one of the best ways to protect ourselves and others from getting sick,” says epidemiologist Dr. Anna Bowen of the Centers for Disease Control and Prevention (CDC).

“Globally we can all be doing better with hand-washing,” she says. Her studies find that children in Pakistan and China missed school less and learned more after intense instruction in hand-washing.