Pigmented contact dermatitis and hair dyes: A retrospective case–control multicentre study in Korea

Background Pigmented contact dermatitis (PCD), a rare variant of non‐eczematous contact dermatitis, is clinically characterized by sudden‐onset brown or grey pigmentation on the face and neck. It is hypothesized to be caused by repeated contact with low levels of allergens. Objectives This study evaluated the risk of using hair dyes in patients with PCD in Korea. Methods A total of 1033 PCD patients and 1366 controls from 31 university hospitals were retrospectively recruited. We collected and analysed the data from the patient group, diagnosed through typical clinical findings of PCD and the control group, which comprised age/sex‐matched patients who visited the participating hospitals with pre‐existing skin diseases other than current allergic disease or PCD. Results Melasma and photosensitivity were significantly more common in the control group, and a history of contact dermatitis was more common in the PCD group. There were significantly more Fitzpatrick skin type V participants in the PCD group than in the control group. There was no significant difference in sunscreen use between the groups. Using dermatologic medical history, Fitzpatrick skin type and sunscreen use as covariates, we showed that hair dye use carried a higher PCD risk (odds ratio [OR] before adjustment: 2.06, confidence interval [CI]: 1.60–2.65; OR after adjustment: 2.74, CI: 1.88–4.00). Moreover, henna users had a higher risk of PCD (OR before adjustment: 5.51, CI: 4.07–7.47; OR after adjustment: 7.02, CI: 4.59–10.74), indicating a significant increase in the risk of PCD with henna dye use. Contact dermatitis history was more prevalent in henna users than in those using other hair dyes in the PCD group (17.23% vs. 11.55%). Conclusion Hair dye use is a risk factor for PCD. The risk significantly increased when henna hair dye was used by those with a history of contact dermatitis.