Believe it or not, as with adolescent acne, hormones are believed to be mainly to blame. In the case of newborns, however, it’s not their own hormones that are probably prompting the pimple problems, but Mom's — which are still circulating in baby's bloodstream as a holdover from pregnancy. These maternal hormones stimulate baby's sluggish oil-producing glands, causing pimples to pop up on the chin, forehead, eyelids and cheeks (and, sometimes, the head, neck, back and upper chest).
Diet. Studies indicate that certain dietary factors, including skim milk and carbohydrate-rich foods — such as bread, bagels and chips — may worsen acne. Chocolate has long been suspected of making acne worse. A small study of 14 men with acne showed that eating chocolate was related to a worsening of symptoms. Further study is needed to examine why this happens and whether people with acne would benefit from following specific dietary restrictions.