Biotin
"Worst supplement I EVER took. I developed cystic acne. Large pimples continued to develop even after I stopped taking the Biotin. I could not believe how huge the cysts formed under my skin. My chin literally was deformed with the cysts. I had one on my left side of the chin and one on my right. They were the diameter of a dime and massively swollen. I was so embarrassed, there was nothing to make them go away. I continue to get small cysts of acne randomly on my face, I never had acne like this before. DO NOT take this product. Terrible doesn't begin to describe it....and reducing the symptoms by drinking water with it does not help, nor taking a b vitamin, as people suggest."