HMOX1 and vitiligo: Consistent with these results, when the serum HO‐1 activity was divided into tertiles, individuals with the 0 risk allele and HO‐1 activity in the upper tertile (>43.6 pg/ml) had a larger decrease in vitiligo risk (adjusted OR = 0.41, 95% CI = 0.20–0.85) compared to those with the 1‐2 risk allele and lower tertile HO‐1 activity (≤26.3 pg/ml).