Allergy to colophony (rosin)

The image shows a well-demarcated blistering eruption around a recent surgical wound, with some extension of erythema onto surrounding skin. The dermatitis was initially thought likely to be due to the skin cleanser used prior to the procedure or to the dressing applied afterwards. However, patch testing (figure 2) revealed contact allergy to colophony (rosin), a balsam or sticky material derived from pine trees. The dermatitis was caused by Friar's balsam (benzoin compound tincture), which had been applied prior to adhesive strips used to support the wound.