Whether there is a causal relationship between milk intake and acne is unknown. We tested the hypothesis that genetically determined milk intake is associated with acne in adults using a Mendelian randomization design. LCT-13910 C/T (rs4988235) is associated with lactase persistence (TT/TC) in Northern Europeans. We investigated the association between milk intake, LCT-13910 C/T (rs4988235), and acne in 20,416 adults (age-range: 20–96) from The Danish General Suburban Population Study (GESUS). The adjusted observational odds ratio for acne in any milk intake vs. no milk intake was 0.93(95% confidence interval: 0.48–1.78) in females and 0.49(0.22–1.08) in males aged 20–39 years, and 1.15(95% confidence interval: 0.66–1.99) in females and 1.02(0.61–1.72) in males above 40 years. The unadjusted odds ratio for acne in TT+TC vs. CC was 0.84(0.43–1.62) in the age group 20–39 years, and 0.99(0.52–1.88) above 40 years. We did not find any observational or genetic association between milk intake and acne in our population of adults.