This hand belonged to a postman. Close questioning revealed that he wrapped groups of letters in large thick elastic bands and then used other elastic bands to hold the bundles of letters in that hand when he was delivering from door to door.
Patch testing showed an allergy to mercaptobenzothiazole, a rubber allergen found in elastic bands. Use of a strong topical steroid cream and changed work practices not involving the use of rubber bands led to disappearance of the problem. Patch testing is a very useful technique to determine the likely allergen in a situation like this.
For patch tests results, log into www.skinconsult.com.au