Why do teenagers have so many pimples?

I remember when I was 13-17 I had pimples all over the place. I never stopped getting them completely, but around 18 or 19 I would only get a pimple once a month or less. I know puberty has something to do with it, but in health class they never told us why puberty causes pimples. Can anyone give me an explanation?

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Answer:
During Adolescence, many teenagers at least once have to experience pimples. Hormones, when you have mood swings it might be causing stress or if you just don't feel good about your self or your body during puberty you get stressed and sooner or later your stress turns into pimples. Pimples can be caused by clogged pores. But, most of the time its not caused by it during adolescence it can but most of the pimples you get are from stress.

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Answer:
the release of hormones in puberty leads to acne however it is caused by a bacteria so there is a missing link i'm not sure what it is

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Answer:
All the hormones are running crazy so it creates extra oil in your face area, causing acne.