Hi! I am healing my acne and I asking myself this question, too. For me, I think every person have different genetic prepositons, like Sonia said, and bad and unhealthy diet can causes different diseases/problems to everyone. For example, I can eat what I want, such as fatty sweets all day long, and I would be still slim, probably. But it causes me acne. For some people it causes them fat althoug their skin can be perfect. And some with strong digestion may be without problems long time but they can get heart diseases, diabets or cancer later. Every time I don’t feel good about it I calm down because starting and living healthy lifestyle is always the best solution that you will appreciate later 😉 I am sorry for any mistakes, I am not native english speaker, but I hope that it will help!