For me chocolate causes acne (usually on my back). It happens to my father too. When I eliminate that one item from my diet I am fine. Every few years I eat chocolate in hopes that my body's reaction will change. But 30 years later it still causes a reaction.

My high school health teacher insisted that chocolate does not cause acne, according to the research. Her definitive statement made me ignore what my father had been telling me for years. That's the problem with health science, you never know if you are an outlier to which the research does not apply.