Pigmented contact dermatitis (PCD) is a variant of contact dermatitis, in which brown-gray reticulated pigmentation is the main symptom rather than typical eczematous changes. We present two cases of PCD caused by pure henna.

A 60-year-old woman presented with reticulated, grayish hyperpigmentation over her face, with mild erythema (Fig. 1A). We received the patient's consent form about publishing all photographic materials. She used a natural henna-based hair dye (Hennaking™; NaturalHealthKorea, Seoul, Korea) 2 months prior, with lesions developing after the second use. Histopathological examination revealed vacuolar degeneration of the epidermis and numerous dermal melanophages (Fig. 1B, C). Patch testing with the Korean standard series (KOR-1000, Chemotechnique®; Chemotechinique Diagnostics, Vellinge, Sweden), as well as her cosmetics and her hair dye (red henna powder 20% aqua), was positive to potassium dichromate (+/+, D2 and D4) and red henna (±/+), and negative to other compounds, including ρ-paraphenylenediamine (PPDA). The henna-based dye was analyzed by Safety Monitor Corps Eco Friendly Lab Inc. (SEL Inc., Asan, Korea; http://www.sel.re.kr) and no chromium or chrome salts were detected. She was diagnosed with PCD due to the henna-based hair dye.

A 55-year-old man developed generalized grayish hyperpigmentation on his face and neck, which was precedented by slight erythema with mild pruritus in the periauricular area, after the third use of a natural henna powder hair dye (Radico Angel Henna™; Huencompany, Seoul, Korea) (Fig. 2A). Histopathological findings were consistent with PCD (Fig. 2B, C). Patch test results were positive for potassium dichromate (+/+) and red and brown henna powder in 20% aqua (±/+), and negative for other compounds, including PPDA.

Henna contains the pigment lawsone (2-hydroxy-1,4-naphthoquinone), which interacts with keratin to yield a reddish-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 dyes1.

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 spongiosis2. 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)3.

These case reports have important clinical implications in that pure henna, popular owing to its low allergenicity, also poses a risk of contact dermatitis.