Five cases of allergic contact dermatitis caused by <scp>Basic Blue</scp> 99 contained in hair colour treatment products

Basic Blue 99 (CAS no. 68123–13-7) is a type of dye contained in hair colour treatment products. While there have been reports of immediate-type allergies, reports of contact dermatitis are few. In Japan, there is a high need for hair dyes that colour hair black. Hair colour treatment products have become widely used by patients with allergic contact dermatitis to substances like paraphenylenediamine, or by those wishing to avoid such reactions. It is a troublesome issue when contact allergies occur from hair colour treatment products used to avoid allergies. We report five cases of allergic contact dermatitis caused by Basic Blue 99 contained in hair colour treatment products that we encountered over a recent 3-year and 3-month period from March 2021 to June 2024. For patch testing, Finn Chambers® on Scanpor tape® were used; occlusive exposure was for 48 h. Conforming with ICDRG standards, readings were performed on Day (D) 2, D3 and D7 or D8. We used Basic Blue 99 1% pet obtained from the company marketing the hair colour. We also included the participants' own semi-permanent hair dye as used by them in terms of open tests. The cases involved one male and four females aged 51–81 years, all of whom developed eczema on the head after using hair colour treatment products. In two cases, the condition was also observed on the face, and in one case, on the trunk. Patch tests with 1% Basic Blue 99 showed positive reactions of + to ++ according to ICDRG criteria in all five cases. Open tests with the hair colour treatment products used were also positive in four cases. Among these, three cases were positive to paraphenylenediamine, and two cases were positive to p-methylaminophenol sulphate (Table 1). Basic Blue 99 has been in production since 19911 and is used in hair colour treatment products at concentrations of 0.004%–2%.2 it is an impure direct dye mixture (a mixture of 23–32 substances at various concentrations and with varying composition) in temporary or semi-permanent hair dye formulations, with a maximum on-head concentration of 1.0% (Scientific Committee on Consumer Safety [SCCS] Opinion on Basic Blue 99 [CO59]-SCCS/1585/17-Final Version, June 2017). Because of the complex and batch-variable composition, the SCCS could not conclude on its safety, not even up to a 1% concentration on-head (lower than the concentration allowed in other parts of the world). Regarding the sensitization potential of Basic Blue 99, Søsted et al.3 examined the predicted sensitization values of 229 hair colouring-related substances and reported that Basic Blue 99 has an equal or higher potential than paraphenylenediamine. While this result is based on predictions from chemical structure and may differ from actual biological reactions, it suggests that Basic Blue 99 cannot be considered safe. While there have been reports of immediate-type allergies,1, 4-6 reports of contact allergies to Basic Blue 99 are few.7-9 In the report by De Groot A C et al.,7 1% Basic Blue 99 was used for patch testing, and it was reported to be negative in 25 healthy control subjects. Iwasaki et al.9 reported a case of severe allergic contact dermatitis accompanied by fever and mucosal symptoms. The five cases reported here did not show symptoms of immediate-type allergy or systemic symptoms. Of the five cases reported here, four had a history of contact dermatitis from oxidative hair dyes, and many showed positive patch test results to allergens other than Basic Blue 99. As consumers become more aware of the risk of contact allergies from oxidative hair dyes, the market for alternative colour treatment products may expand, potentially increasing the number of patients. It will be necessary to add Basic Blue 99 as one of the patch test allergen for hairdressing series, and to further clarify which of the mixed components is the responsible allergen. Kazue Nishioka: Conceptualization; investigation; writing – original draft. Akiko Koizumi: Investigation. Yuko Takita: Investigation. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author (Kazue Nishioka) upon reasonable request.