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Vol. 30, No. 6, 2018 737 Received September 25, 2017, Revised November 13, 2017, Accepted for publication December 31, 2017 Corresponding author: Kyung Eun Jung, Department of Dermatology, Eulji University Hospital, Eulji University School of Medicine, 95 Dunsanseo-ro, Seo-gu, Daejeon 35233, Korea. Tel: 82-42-611-3035, Fax: 82-42-259-1111, E-mail: [email protected] ORCID: https://orcid.org/0000-0003-0968-1079 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/ licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Copyright © The Korean Dermatological Association and The Korean Society for Investigative Dermatology dish-brown color. Unlike red henna, brown henna contains indigo plant leaves and black henna contains PPDA, a well-known contact allergen. Red henna, without any additives, has low allergenic potential and is considered a safer alternative to conventional PPDA-containing hair dyes. Both patients developed extensive hyperpigmentation following mild erythema after using henna-based hair dyes. Post-inflammatory hyperpigmentation, Addison’s disease, friction melanosis, and drug eruption were excluded from differential diagnoses due to the absence of prior inflammation or hyperpigmentation in the skin creases, and no history of nylon towel on the face or drug use. Patch testing revealed that pure red henna was the causative allergen. The hyperpigmentation gradually faded after discontinuation of henna product use and treatment with topical tacrolimus and oral tranexamic acid. Although the exact pathophysiology of PCD is unclear, it is proposed that persistent contact with low level chemicals causes cytolysis in the basement membrane, resulting in pigment incontinence without overt spongiosis. We speculate that traces of henna remained on the scalp and hair after washing, and acted as a persistent allergen. This is consistent with the observed prominent pigmentation on the neck and face of the second patient who washed his hair in a standing position. We found a single report of PCD caused by pure red henna (Queens Henna; NTH Co. Ltd., Tokyo, Japan). These case reports have important clinical implications in that pure henna, popular owing to its low allergenicity, also poses a risk of contact dermatitis.