- Area is a little extra warm to touch.
- You may feel feverish.
- Red blotchines at the surface of the skin.
An abcess starts off from an infection. This is what happens with injections. If there is bacteria in the oil, on the skin or on the needle, it could find it's way inside your muscle. Then the infection begins. It usually starts off as cellulitis, which is a moderate infection that the body starts to fight off like any other infection. If the bacteria is too strong or too much, the body will protect itself by enclosing the infected area with a hard shell to contain it. This is the abcess. It needs to be surgically removed unfortunately as it is useless tissue at that point. The bigger the infection the bigger the abcess.
So to answer your question, an abcess is caused by an infection. An infection could have been caused by bacteria entering the muscle via the needle, or the oil. That is why we all stress on sterility of injection sites, needles, and oil