Okay, so you know how when you go to the doctor or hospital, they clean their hands with soap and water or use a special cleaning liquid like hand sanitizer? That is because we need to be clean and prevent germs from spreading.
Well, a long time ago, a man named Ignaz Semmelweis was a doctor in a hospital, and he noticed that lots of women were getting sick and even dying after giving birth. He thought and thought about why this was happening and finally figured out that the doctors and nurses were not washing their hands between patients.
Lots of people didn't believe him or want to change their ways, but he kept telling them that washing hands was really important to preventing germs from spreading. Eventually, people realized he was right and started cleaning their hands between patients. This helped save lots of people's lives and made hospitals a safer place.
So, Ignaz Semmelweis was a smart man who found out something really important to keep people healthy - washing hands is super important!