Contact Urticaria Caused by Ultrasound Gel Containing Phenoxyethanol in a 4‐Year‐Old Boy

We report herein the first paediatric case of phenoxyethanol-induced contact urticaria triggered by ultrasound gel, which underscored the importance of recognising potential allergens in routine diagnostic procedures, including those involving young children. A 4-year-old boy was admitted with suspected systemic juvenile idiopathic arthritis (sJIA). After therapy with oral naproxen and intravenous corticosteroid was begun, cardiac ultrasound was performed to assess for serositis. During the procedure, clear, pale wheals with surrounding erythema developed on the anterior chest at the gel application site (Aquasonic 100; Parker Laboratories, Fairfield, USA) (Figure 1) and improved within 30 min following the administration of an H1 blocker. The gel contained reverse osmosis water, humectant, polymer, water-soluble fragrance, FD&C colours, phenoxyethanol, and ethylhexylglycerin. Although the patient had no history of allergies, history-taking revealed similar symptoms during echocardiography and at the age of 2 years following the use of shampoo and soap. After sJIA was diagnosed and canakinumab therapy was begun, skin prick tests (SPTs) were performed with Aquasonic 100, phenoxyethanol (FUJIFILM Wako Pure Chemical Co., Tokyo, Japan; liquid form), and ethylhexylglycerin (Tokyo Chemical Industry Co. Ltd., Tokyo, Japan; liquid form). The last two ingredients were contained in the shampoo and soap, which previously triggered a similar reaction in our patient. Table 1 summarises the results of the tests. All SPT results were evaluated after 15 min. A 10-mm and 4-mm wheal developed after the application of Aquasonic 100 and undiluted phenoxyethanol, respectively. Diluted phenoxyethanol and all concentrations of ethylhexylglycerin were negative. SPTs with the shampoo and the liquid hand soap that the patient had previously used produced a wheal 5.5 and 21.5 mm in size, respectively, and a positive and negative control produced a wheal 4 and 0 mm, respectively. A healthy control subject underwent a SPT with all the substances listed in Table 1 and was negative for each. Aquasonic 100 produced a larger wheal (10 mm) despite containing phenoxyethanol. A positive response to undiluted phenoxyethanol (4 mm), together with the patient's clinical history of recurrent reactions to phenoxyethanol-containing products, suggested that phenoxyethanol was the most likely causative agent. The clinical course and SPT findings led to the diagnosis of immunological contact urticaria to phenoxyethanol. As no later readings (e.g., at 30 min) were performed, the possibility that additional reactions might have occurred after 15 min was unable to be ruled out. Subsequent ultrasound examinations were safely performed using a water-filled glove instead of gel. The patient's parents were advised to prevent their child from using phenoxyethanol-containing products. Phenoxyethanol, a preservative commonly found in personal care products, can cause contact urticaria [1-3]. Furthermore, while some ultrasound gels contain phenoxyethanol, they rarely cause contact urticaria [4]. In the present case, urticaria recurred upon contact with ultrasound gel. Notably, similar symptoms had been observed during the patient's first echocardiographic examination in early childhood, suggesting that sensitization to phenoxyethanol may have occurred through previous exposure to the substance in personal care products, such as shampoos or soap. The positive SPT results for the shampoo and hand soap (tested ‘as is’) in this case might have indicated irritation induced by surfactants or other substances. However, additional testing with phenoxyethanol-free shampoo and soap yielded a negative result, indicating that this chemical was most likely the causative agent, although the involvement of other ingredients was unable to be ruled out [5]. The findings of this study demonstrated that even if ultrasound is a generally safe procedure, substances contained in ultrasound gel can occasionally trigger contact urticaria in children. A phenoxyethanol-free gel should be the first choice for patients with suspected phenoxyethanol allergy. In urgent situations where the causative allergen is unknown or phenoxyethanol-free gel is unavailable, a water-filled glove can serve as a safe and practical alternative, as shown in this case. In this technique, the ultrasound probe is applied to the skin through a glove filled with water, which functions as a coupling medium. Reiko Yatabe: conceptualization, investigation, writing – original draft. Naoki Kajita: conceptualization, investigation, writing – original draft, supervision. Keiji Akamine: conceptualization, investigation, writing – review and editing, supervision. Riku Hamada: writing – review and editing, supervision. Koichi Yoshida: writing – review and editing, supervision. We thank James R. Valera, our in-house editor and an employee of the Tokyo Metropolitan Children's Medical Center, for his help with editing and proofreading the manuscript, and Tatsuo Kono for providing expert guidance on ultrasound imaging. Written consent for the publication of the details of this case was obtained from the patient's parents. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.