When I was in HS in the final grade a girl liked me and I didn't like her. I explained to her why and calmed her and after a few days I noticed that she started having acne, similar to the way I had acne when the same thing happened to me.

I think this is hormonal which is a reason why teenagers upon reaching 18 should find a girlfriend. The longer time you don't have someone... the more acne you have. If you see someone with a lot of acne: They're lonely.

Of course I am no medical professional so anything I say can be taken lightly.