I have very bad acne mainly on my forehead and it has been this way since I was about 11 years old (I'm 16). I was diagnosed with Hypothyroidism when I was 7 and from that pointon I developed a few pimples every now and then. Then when I was 14 I was diagnosed with Hashimoto's disease as well and my acne has gotten worse. I eat a healthy gluten free and dairy free diet, get enough sleep, drink lots of water, and exercise regularly so the only thing I can guess it is caused by is the thyroid problems I have but at the same time anyone I know with similar thyroid problems doesn't have acne.