Physical Danger
Almost everyone who works in a hospital is at risk of catching something gross thanks to contaminated fluids or needle sticks. There's never a dull moment when you're taking care of people who are sick or in life-threatening conditions.
If you work in a lab, though, your pace will be a little less harried, so the kind of accidents that come from rushing around typically won't be a problem for you. Following strict lab protocols will help keep you safe, too.