Hair care products are a major source of lifestyle-related chemical exposure in the general population, especially since hair dye use is becoming an integral part of modern culture12. Hair dyes are usually used to conceal gray hair or to change hair color and hair dyeing is frequently performed in Korea34. Kim et al.5 reported that 63.8% of the Korean population has dyed their hair. Allergic contact dermatitis (ACD) from hair dye is a worldwide problem of individuals who dye their hair16. P-phenylenediamine (PPD) is the most frequent contact sensitizer present in hair care products and is a primary patch test screening agent for hair dye contact allergy (HDCA)2367. The clinical findings of hair dye allergy vary and include typical ACD, lichen simplex chronicus, non-specific eczema and dermographism on the hair dye-exposed area or/and extended area6. In severe cases, acute systemic adverse effects such as angioedema, upper airway obstruction, rhabdomyolysis, and acute renal failure have also been reported2. We investigated 105 patients with hair dye allergy with a positive PPD patch test result to identify the clinical characteristics of hair dye allergy and to clarify the relationships between hair dye allergy, duration of hair dye use, and frequency of hair dye use.

PPD is an aromatic amine that is used for hair dyes and henna tattoos8. PPD is also a common allergen and is commonly suspected to be the cause of HDCA9. In European, North American and Asian general populations, 1 to 6% of all patients with dermatitis have been reported to be sensitized to PPD; these percentages rise to 38% to 97% in patients with hair dye dermatitis810. Another study reported a median prevalence of PPD sensitization in Asia of 4.3%9. High positive reactivity rates to PPD have been reported in Korea1112131415. These high rates seem to be related to the increased demand for hair coloring and the trend for individuals to begin using hair dye for cosmetic purposes at a relatively young age. Henna tattoos might also be an important source of PPD exposure and sensitization11617.

Our study found a higher prevalence in women (70.5%) than men, similar to the findings of previous studies9161819202122. This finding reflects the higher exposure of women23. In a European cross-sectional study of individuals from the general population, 50.9% of all individuals were found to have used hair colorants at least once in their lifetime; 78% were female and 20% were male24. In a study conducted in Korea, women (57.8%) showed higher prevalence than man (42.2%) similar to our study9.

The prevalence was higher in older patients, particularly individuals over 50 years of age (66.7%). In Korea, the onset of hair graying usually starts in the third or fourth decade of life25. In a study conducted in Korea, patients over 50 years of age showed higher prevalence (86.7%) similar to our study9.

We also analyzed the clinical symptoms and signs of patients with HDCA. The most commonly observed symptom was pruritus (71.3%). Pricking sensations (8.6%), dryness (1.9%) and burning or tingling sensations (1.0%) were also detected. Among the clinical signs evaluated, erythematous macules and patches were observed on 59 patients (56.2%) and second most common sign was erythematous papules and plaques (7.6%). Our findings are similar to those of previous studies. Kim et al.5 reported that pruritus was the most common side effect related to hair dye use; eye tingling sensations, erythema, scales, vesicles, oozing, edema, and swelling were also reported. The clinical features of HDCA vary from mild contact dermatitis in a localized area or disseminated generalized dermatitis to severe complications including contact urticaria, angioedema, erythema multiforme-like lesions, hair loss, rhinitis, bronchospasms, asthma, and renal toxicity, the latter of which can be life threatening2627. Dermatologic problems like atopic dermatitis are also potential risk factors for contact sensitivity because the impaired skin barrier leads to increased allergen penetration28.

We found that the face (57.1%) was the most frequently affected site, followed by the scalp (36.2%) and neck (34.3%). Similar result was reported in the study conducted in Korea. Lee et al.9 reported the face as the most frequently affected site, followed by the scalp. We grouped the face, scalp, and neck as direct contact areas and other areas such as the trunk, hand, upper extremities, lower extremities, and feet as indirect contact areas. In our study, 68 people (64.8%) had HDCA only on the direct contact area, while 37 people (35.2%) showed skin lesions on both the direct and indirect areas. Similar to our study, other studies have reported that the forehead was the most common location showing an allergic reaction to PPD, followed by the eyes, ears, and then scalp; these direct contact areas also showed more severe presentation9172129. Allergy contact dermatitis from PPD derivatives also seems to be related to lichen planus or lichenoid eruptions6303132. In another study, Chey et al.6 reported that patients with hair dye ACD and combined chronic skin lesions such as lichen simplex chronicus showed chronic skin lesion improvement after discontinuing hair dye use.

A total of 52 patients (49.5%) had multiple skin problems. Eczematous lesions (25.7%) including nummular eczema, pompholyx and hand eczema were the most common.

The second most common problem was urticaria (14.3%), including acute or chronic urticaria, symptomatic dermographism and solar urticaria. Prurigo simplex or prurigo nodularis (8.6%), seborrheic dermatitis (7.6%) and lichen simplex chronicus (2.9%) were also detected.

Many studies have reported that individuals with ACD may develop more severe allergic reactions when exposed to causative allergens and that increases in exposure duration and frequency might lead to more severe clinical presentation9. We observed that skin lesions were more widespread in patients who had longer exposure time to hair dye. However, exposure time to hair dye was not significantly correlated with PPD patch test reactivity. Similarly, exposure time to hair dye was not significantly correlated with the number of combined skin lesions. The absence of observable significant correlations might be due to the small number of patients in this study; further large-scale multicenter studies are needed to test this hypothesis.

Most patients (80%) were recognized or suspected of having hair dye allergy before the patch test diagnosis. However, only 28.6% of the patients stopped hair dye use, even after diagnosis was confirmed. For effective treatment of HDCA, it is important to properly educate patients with HDCA about the clinical manifestations of HDCA and to keep away from allergens.

This study is important because we focused on the clinical characteristics of HDCA and the relationships between exposure time to hair dye, severity of HDCA, and combined skin disease.

Our study does have some limitations. First, it could have selection bias and/or recall bias, since it was conducted at a university hospital in a retrospective manner. Second, we only studied PPD as an allergen causing HDCA. However, widely used commercial hair dyes include many other allergens and individuals with allergic reactions to PPD have been reported to show frequent cross-reactions with other dyes, local anesthetics, and black rubber antioxidants1633. Since the number of patients in this study was relatively small and the study was not conducted across the entire Korean population, further large-scale multicenter studies are needed.