This is a common myth but it is untrue. Diet can affect your acne. Two problematic studies that were done in the 60s and 70s found that chocolate was not a cause of acne. These studies were widely read and accepted so not many other studies were conducted. [1] Today researchers have found that certain foods can make your acne worse. Some foods include: chocolate, bread, green tea, milk, white sugar, ripe banana, ice cream, apple, orange, and red meat consumption. [2]
[1] Jennifer Burris, MS, et. al. Acne: The Role of Medical Nutrition Therapy, March 2013Volume 113, Issue 3, Pages 416–430
[2] Karadağ AS, et al. The effect of personal, familial, and environmental characteristics on acne vulgaris: a prospective, multicenter, case controlled study from Turkey. G Ital Dermatol Venereol. 2017 Jul 11.