**5.3.3 Heparin**

Heparin is a sulfated glycosaminoglycan with anticoagulant properties. It is usually injected intravenously or subcutaneously but is also available for topical application. Cutaneous allergic reactions due to subcutaneously injected heparin have been reported **[49-50].**

We report a case of patch-test-negative allergic contact dermatitis, diagnosed by scratch patch testing, from a gel containing heparin. Allergic reaction to subcutaneously injected heparins is not a rare occurrence **[51-52]** but there are only a few reports of contact dermatitis from topical heparin **[53].**

In cases of suspected contact allergy, when conventional closed patch test shows negative or doubtful results, scratch–patch testing should be considered. We recommend, after performing scratch-patch test, to execute a ROAT to be sure the drug can be applied safely.
