Contact Dermatitis From Natural Indigo (Indigofera Tinctoria Leaf Extract) Contained in Hair Dye Preparations: A Case Series

Allergic contact dermatitis (ACD) to hair dyes is commonly caused by para-phenylenediamine (PPD) and related chemicals. We report three cases of ACD to hair dyes containing natural indigo. A 48-year-old woman presented with a scalp dermatitis that occurred after the third use of a natural hair dye. She was patch tested using IQ chambers (Chemotechnique Diagnostics, Vellinge, Sweden) with the European baseline series, with several supplemental series, including our hairstyling panel (25 hairstyling-associated allergens), plant (15 allergens) and cosmetic (50 allergens) batteries, and different hair dyes (brown, dark brown and hazelnut, Hairborist BVBA, Belgium) used by the patient. Patch tests were positive (+) at day 3 (D3) for ‘brown’ powder, ‘dark brown’ powder, and ‘hazelnut’ powder, in 30% and 50% petroleum (pet), confirming contact allergy to natural dyes (Figure 1). All others patch tests were negative. As these three hair dyes shared two allergens, Lawsonia inermis leaf extract (LILE) and Indigofera tinctoria leaf powder (ITLP), these two allergens (kindly provided by Hair Borist BVBA, Belgium) were then tested. Patch tests in 50% pet and open tests (in 50% pet and water) were positive (+) for ITLP and negative for LILE at D3 (Figure 2). The patch test for ITLP was negative in water. A 63-year-old woman, with known allergy to Patent Blue V, was tested for several episodes of scalp pruritus and facial dermatitis (Figure 3) after application of natural hair dye. Patch tests in IQ chambers (Chemotechnique Diagnostics, Vellinge, Sweden) for European baseline and hairdressing series, and for patient's natural hair dyes (Rajasthan henna, dark chestnut henna and auburn henna, Aroma-Zone, France) were performed. The patch tests for ‘dark chestnut henna’ and ‘auburn henna’ in 30% pet were doubtful at D3, but were positive (+) at day 5 (D5) both in 30% pet and water (Figure 4). All other tests were negative. Whilst the Rajasthan henna product is simply the finely powdered dried leaf from L. inermis, the ‘dark chestnut’ and ‘auburn henna’ products contained the cosmetic product ingredients LILE and ITLP. So, patch testing with both LILE and ITLP was then carried out. ITLP in pet was positive (+) at D3 and (++) at D5 (Figure 5). ITLP in water and LILE were negative. A 46-year-old woman complained of scalp pruritus immediately after natural hair dyeing. The following day, she developed a scalp dermatitis, which lasted a week. The patch tests in IQ chambers (Chemotechnique Diagnostics, Vellinge, Sweden) for European baseline, hairdressing, cosmetic, plants and essential oils series were negative at day 2 (D2) and day 4. Patch tests for ITLP in water were positive (+) at D2 and doubtful at D3, whereas patch tests for ITLP in pet and LILE were negative. Unfortunately, no delayed reading was possible. Prick tests for both extracts at D2 and D3 were negative. We report three rare cases of contact allergy to natural indigo (I. tinctoria Leaf Extract) contained in hair dye preparations. I. tinctoria is a species of plant in the Fabaceae plant family. When macerated with water, its leaves release a blue dye, indigotin, from a colourless precursor glucoside named indican. Allergy to standard hair dyes is well known, with strong allergens such as paraphenylene diamine and paratoluene diamine. Our cases demonstrate the pitfalls of hair dyeing. Allergy to natural hair dyes is less well known, as it occurs much less frequently, particularly in Europe. To our knowledge, only two other cases of contact dermatitis to natural indigo powder, derived from the I. tinctoria plant, have been described [1, 2]. However, a cross-sectional Indonesian study conducted on 63 batik workers demonstrated the high prevalence of allergies to natural dyes including, I. tinctoria, sappan wood (Caesalpinia sappan), and mahogany (Swietenia mahagoni) compared with common allergens such as PPD [3]. Indigo hair dyes can also cause occupational asthma, rhinitis, and contact urticaria [4]. For this reason, allergies to natural hair dyes should not be ignored. In our three cases, patch test positivity was delayed to day 3–5 as compared to the usual delay of 2 days with the usual tinctures. Late readings are therefore recommended to avoid doubtful or false-negative patch tests with I. tinctoria leaf powder [1, 2]. Furthermore, patch test modalities (dilution, vehicles: water or pet) remain to be defined/optimised [5]. We present these cases to raise awareness of natural indigo from I. tinctoria as a potential contact allergen and to reiterate the importance of patch testing to personal products. Angéline Charansol: writing – original draft, investigation. V. Bourdenet: writing – review and editing, validation. Anatole Hanniet: writing – review and editing, validation. Fabien Pelletier: writing – review and editing, validation. François Aubin: writing – review and editing, validation. Florence Castelain: supervision, writing – review and editing, validation. We would like to thank Hair Borist BVBA, Belgium who kindly provided Lawsonia Inermis Leaf Extract and Indigofera Tinctoria Leaf Powder for patch testing. The patients gave written consent to publish their case details and photographs. The authors declare no conflicts of interest.