An Unusual Cause of Allergic Contact Dermatitis in a Postoperative Patient

Friar's Balsam or compound benzoin tincture is used for its antiseptic and protective properties for treating abrasions and minor lacerations. In some clinical situations, Friar's Balsam is also used in surgical dressings for its combined antiseptic and adhesive properties. We report a case of severe allergic contact dermatitis in a patient due to Friar's Balsam used to improve skin adhesion of dressings after varicose vein surgery.

A 40-year-old female was referred to the dermatology clinic in July 2022 for assessment of a cutaneous reaction on her right lower limb (Figure 1). A rash developed within 48 h of routine varicose vein surgery. She underwent patch testing to the British Society for Cutaneous Allergy (BSCA) standard, facial, fragrance, medicaments and methacrylates series. Patch tests were applied with IQ Ultra chambers with medical-grade adhesive tape and read at 48 and 96 h. She was additionally tested to steristrips and cicaplaie dressing. She had 1+ positive patch test reactions to fragrance mix I (8.0% wsp), M yro xylon p ereirae (25% wsp), cinnamic alcohol (2.0% wsp) and jasmine absolute (2.0% wsp), but not to the aforementioned dressings. Based on these results, she was diagnosed with fragrance allergy and irritant reactions to dressings. In 2024, she was referred again by vascular surgery following a similar, more severe reaction on the left lower limb following varicose vein surgery. She underwent repeat patch testing to the BSCA standard series, in addition to facial, fragrance and medicaments series. We also patch tested with honeycomb dressing, which was used instead of Mepore dressing on this occasion. Following careful review of the dressing procedure with the vascular surgeon, we ascertained that no glues were used in the surgical procedure but that Friar's Balsam was applied to the skin before the overlying dressing. On this occasion, she had 1+ positive patch test reactions to Myroxylon pereirae (25% wsp), fragrance mix I (8.0% wsp), oxidised linalool (0.5% wsp), cinnamic alcohol (2.0% wsp), isoeugenol (2.0% wsp), narcissus absolute (2.0% wsp) and jasmine absolute (2.0% wsp), and a (3+) reaction to a sample of neat Friar's Balsam applied to the abdomen (Figure 2). There was no reaction to neat Friar's Balsam applied to the abdomen of 10 control subjects.

Friar's Balsam is a traditional topical and inhaled topical medication made from a mixture of benzoin resin, tincture of benzoin, and other ingredients [1]. It was once widely used in surgery and wound care, before advancements in antiseptic and antimicrobial therapies. It was thought to reduce the risk of infection and improve dressing adherence. It is also known for its use as a home inhaled remedy for respiratory conditions [2].

Friar's Balsam or Compound Tincture of Benzoin is derived from natural resins. The main constituents are benzoin resin (contains benzoic acid, benzyl benzoate, and vanillin), Balsam of Tolu (contains cinnamic acid derivatives) and storax (styrene-based compounds). Essential oils such as myrrh and aloe feature, in addition to ethanol, which acts as a solvent for dissolving resins and enhancing compound preservation. The plant origins of Friar's Balsam trace back to tropical trees like Styrax benzoin (benzoin resin) and Myroxylon balsamum (balsam of Tolu and Peru). These trees are native to Southeast Asia and Central/South America, respectively [3].

There are previous case reports of contact allergy to Friar's Balsam in the literature. One such report describes an anaesthetist who developed an acute blistering reaction to aerosolized Friar's Balsam when spraying it to improve dressing adherence following a spinal anaesthetic procedure [4]. There are also reports of allergy to tincture of benzoin [5, 6], with additional reports of cross-reactivity to similar allergens such as fragrance mix, balsam of Peru, colophony and tea tree oil [7].

In our case, it is likely that prior sensitisation to fragrances resulted in a cross reaction to the allergens in Friar's Balsam.

Julia O'Mahony: writing – original draft, investigation, methodology, writing – review and editing, project administration. YiXuan Goh: writing – review and editing. Anne Lonergan: resources, investigation. John Bourke: writing – review and editing, supervision, investigation, methodology.

Patient consent has been given to include images in the case report for publication.

The authors declare no conflicts of interest.