Everyone knows hand washing is important. But a new study shows how washing your hands often, and at the right time, can have a big impact on your family’s risk for getting sick.

Most studies on hand washing focus on medical and food service workers. But this month’s American Journal of Infection Control focuses on washing hands at home as a way to stop infections from spreading. Several studies show hands are the single most important transmission route for all types of infections.

Even though most people know to wash their hands after using the toilet or handling a diaper, studies suggest many people are still ending up with germs, particularly those spread by feces, on their hands after leaving the bathroom or caring for a baby.

One study looked in homes of infants recently vaccinated against polio. After vaccination, the virus is known to shed in the baby’s feces. Researchers found the virus on 13 percent of bathroom, living room and kitchen surfaces. While the virus from the vaccine didn’t pose a health risk, the study shows how feces-borne viruses can travel through the home.

Another study found that in homes where salmonella cases had been diagnosed, the bacteria were still lurking in toilet bowls three weeks after the outbreak. Water splashing on the toilet seat was a source of contamination.

Doorknobs, bathroom faucets and toilet flush handles are key sources of germ transmission in the home. That’s why people should focus on cleaning such surfaces regularly and always wash hands after touching them. In one study, a volunteer touched a door handle that had been contaminated with a virus. He then shook hands with other volunteers, and further tests showed he had spread the virus to six people.

The study authors note that the timing of hand washing is key. It’s obvious to wash hands after using the toilet, after sneezing or before eating or handling food. Other crucial times for hand washing are after changing a diaper or cleaning up after a pet, or after touching garbage cans, cleaning cloths, cutting boards, dish rags and utensils that may have come into contact with raw food.

While it may be hard to believe that something as simple as regular hand washing can make a difference in your family’s health, consider what happened in Hong Kong during a 2003 outbreak of SARS, a severe and potentially deadly form of viral pneumonia. The outbreak triggered extensive public and community health measures promoting basic hygiene, including regular hand washing. Not only was the SARS outbreak contained, but other cases of respiratory illnesses, including the flu, dropped sharply.