A student developed acute eczematous contact dermatitis in response to the application of tincture of benzoin to the skin under a cast. This was followed within 48 hours by the appearance of generalized noneczematous exanthem. Analysis led to the conclusion that absorption of benzoin through the skin was responsible for both the contact dermatitis and the exanthem. Patch tests demonstrated an eczematous reaction to benzoin, with cross sensitivity extending to the gums of myrrh, locust, galbanum, gamboge, and olibanum.
Spott DA, Shelley WB. Exanthem Due to Contact Allergen (Benzoin) Absorbed Through Skin. JAMA. 1970;214(10):1881-1882. doi:10.1001/jama.1970.03180100071015