Tooth infection leads to face numbness on left side. Why is that?

Numbness. Sometimes, a tooth infection that is located near a major nerve of the face can cause numbness to that region. This can also be the case of the wisdom tooth infection. But numbness to the face can also be the result of other things too. It is advisable to have it checked by a professional.
Dangerous. You have an abcess, infection, that is rapidly spreading affecting surrounding nerves.