Many people do not believe this, but I believe some people are sensitive to foods and can cause acne. The problem is, it is not just one food and it can be several things. It is so difficult to pinpoint and seriously drove me nuts trying to figure it out. It took me about 2-3 years to figure out what caused me to break out. I would get cystic acne, painful ones. At its worst, I was getting a new painful pimple every day, which would take 2-3 months to heal!! So my face was covered and my back! Then I had a thought to when my skin was actually relatively clear in high school and when I started getting problems with my skin around age 18. What changed? Well, I started eating a lot more junk food, eating breakfast etc. From when I was little I never felt hungry for breakfast so I never ate it, which probable gave my body more time to heal etc. In addition to more junk food, I was eating other additional healthy food. But it was actually the healthy foods that caused me to break out! I can eat McDonalds just fine. But figure out avocados and dark chocolate caused painful pimples around my mouth. Most nuts cause painful acne on my back. Flaxseed oil, causes acne all over my face. Too much soy and rice milk causes acne on my chest. I don't have a problem with dairy, as some people do. I thought I might so I tried alternatives, only to realise they gave me reactions elsewhere. Too much sugars also effect me. But once in a while its fine. Anyways, so after years of trying to figure it out. I found those to be my main culprits. I cut them out and my skin is completely CLEAR. Sometimes I get relaxed about it and eat some avocados bc I love how they taste and after a few days of eating them sure enough painful pimples appear. I am fine to eat an avocado once a month with out reaction, but if I eat it once a day a few times a week I break out. I learned that the flaxseeds and flaxseed oil breaks me out by accident. I was eating it to be healthy and my skin was at its worst. Then I went to visit my sister and brought the flaxseeds and forgot them at her house. Well, after a few weeks of not eating them my skin got a bit better and I was on the phone w my sister, who complained about breaking out like crazy all of a sudden and then she said she was eating some cereal w flaxseeds that I left at her place and it was like bell went off, I realised that was once cause and told her. She stopped eating it and cleared up. Then after that I decided to pay attention to my diet. It took a long time to figure it out, because acne is a delayed reaction when you eat something you are sensitive to. Problem is it can take a day or more to show up. Or you can eat a little and be fine, but if you go over a limit you break out. It took years to figure out. I figured it out around age 24 and now I am 34. I am clear most of the time, but to this day, if I eat nuts I break out on my back, if I eat the other foods I break out on my face. I usually avoid them, but sometimes I will eat them and bam...break outs. It was life changing for me, bc acne was making me depressed. It was so frustrating bc even when I would change my diet to help improve my acne, I would accidentally add something new like soy, flaxseeds etc which would cause more acne!
Everyone is different, try watching what you eat and learning what causes it. Most people do not want to believe this, as it is not easy to figure it out and they don't want to restrict diet. For example some people get break out from drinking soda, but don't want to stop their 1-2 cans a day they drink. Or you can be eating something which is meant to be healthy, but it breaks you out, so you have no clue, because its supposed to be good for the skin, like flaxseeds.