It's not very likely that you will get sick from keeping pet rats.
But you should always follow basic hygiene principles when dealing with any animal, including rats.
You shouldn't put them on your face.
When you've been handling animals you should wash your hands before you do anything else. This is because germs get around from one animal to another animal or person--or from one person to another. Because this happens usually by contact, if you are sensible about it then you are much less likely to get sick.
All this applies to pet rats who are probably fairly safe to start with. It definitely does not apply to other rats.