That's a question without a definitive answer! It's the struggle many people face. The same thing happened to me in the winter, literally out of no where. It could be a number of things; here are a few:

- Skin care: have you changed anything in your routine recently?
- Diet: have you recently made any drastic diet changes?
- Stress: are you going through a period where you are more stressed than usual?
- Lifestyle changes: Any drastic changes in sleep patterns, exercise levels, alcohol consumption, and things like that?
- Hormones: this is the tricky one, and it can play a role whether you are a teen going through puberty or an adult who randomly gets adult acne out of no where!

If you can't think of anything at all that could be causing it, I would head to a doc/derm and see if they can give some insight.

Nothing major that I can think off at all , it's all over my face, I'm 22 this is hard  did you manage to find out what was causing yours ?