A scab appears on a pimple to protect it from becoming worse, and severely infected. If you has a scab on a pimple it's best you leave it alone so it can heal properly.
What not to do:
1) Pick, scabs appear to protect and when you pick the scab off bacteria enters your body and can make you sick.
2) Washing your face with a rag with force, if you use force you'll probably end up taking the scab off.
