Active sensitization of para-tertiary-butylphenol after TRUE test

Active sensitization of contact allergen is an uncommon complication of patch test. Para-tertiary-butylphenol (PTBP) is a component of neoprene-based adhesives used in glued leather goods such as shoes, handbags, belts and watchstraps. Contact allergy to PTBP is frequently seen when the patch test is performed. However, active sensitization to PTBP after the patch test is rare. A 23-year-old female patient came to our clinic with a brownish hyperpigmented patch on the belt position of her belly. Pruritic erythematous papules and vesicles developed on the abdomen when she wore new pants 4 months ago. Under the clinical diagnosis of allergic contact dermatitis, the patient was patch tested with the Thin-layer Rapid Use Epicutaneous Test (TRUE Test®). The result showed strong positive reaction to nickel sulphate and thiomersal both on day 2 and 3 after application. Twenty-nine days after the test, the patient noticed pruritus on the TRUE Test area. Thirty-four days after the test, an erythematous square-shaped plaque studded with tiny vesicles developed at the PTBP patch test site. This strongly suggests that the reaction to PTBP is occurred. She was diagnosed with an active sensitization to PTBP. We report a rare and interesting case of active sensitization to PTBP after TRUE Test®.