The most common cause of a rash on the hands is contact dermatitis. Contact dermatitis occurs when allergens or irritants come into contact with the hands; producing blistering and peeling of the hands. Allergens may be plants, latex gloves, jewellery(nickel), perfumes or others. Iriitants may be soap, detergent or household chemicals.
This article from the American Osteopathic College of Dermatology explains contact dermatitis of the hands:
http://www.aocd.org/skin/dermatologic_diseases/hand_rashes.html