Recently a case series was published describing five teenagers who had all experienced sudden onset of moderate to severe acne. On further questioning, the dermatologist learned that these teenagers had all independently started using whey protein as a supplement for body building prior to the acne. When these young men discontinued the whey protein supplement, their acne improved; for those who then restarted taking whey protein, their acne flared. Why would whey protein lead to acne? Whey protein in nutritional supplements is generally derived from cow’s milk. Whey makes up approximately 20% of the protein in milk (the other 80% is casein). Two larger well-designed studies have examined whether or not cow’s milk consumption is associated with acne in teenage girls and separately in teenage boys. (i.e. does drinking milk or eating cow-milk products cause acne?). Both studies showed a mild, but statistically significant, increase in acne in teenagers who drank more than two glasses of cow’s milk daily compared to teenagers who had less than one serving per week. Associations were slightly stronger for skim milk (compared to whole milk) consumption, which is interesting because there is a higher relative percentage of whey protein in skim milk. What does this mean?