World Hygiene Day is held annually on May 5. The date was cleverly chosen because two sets of five fingers symbolize hands, providing an easy mnemonic for handwashing.

"Have you washed your hands yet?" is a question often asked of children in particular—and met with eye-rolling. Yet it’s important, because bacteria are tiny, invisible to the naked eye, and lurking everywhere. Most are harmless, but some can harm us humans—especially when they’ve developed resistance and can no longer be controlled by many antibiotics.

Proper handwashing plays a key role in limiting the transmission and spread of infections and is the simplest, most effective, and most hygienic measure. The daily use of disinfectants in our normal routine is unnecessary or even counterproductive—after all, the immune system should always have a little work to do.