A skin graft can be partial thickness or full thickness. In partial thickness skin grafts, sheets of skin with the epidermis and a small amount of dermis are harvested using special machines called dermatomes. The donor sites heal from the base up (like a partial thickness burn) and can be re-used once healed. In a full thickness graft, the donor site can only heal from the periphery so is usually closed surgically. This limits the size of a full thickness graft that can be taken. The advantage of full thickness grafts is that the skin often retains its elasticity whereas partial thickness skin grafts often lose this if applied to wounds where all layers of the skin have been destroyed by the burn.