The naked mole rat (Heterocephalus glaber), also known as the sand puppy or desert mole rat, is a burrowing rodent native to parts of East Africa. It has a highly unusual set of physical traits that enables it to thrive in an otherwise harsh, underground environment, including a lack of pain sensation in its skin and a very low metabolism. The naked mole rat is also of interest because it is extraordinarily long-lived for a rodent of its size (up to 28 years) and holds the record for the longest living rodent. Naked mole rats appear to have a high resistance to cancer; cancer has never been observed in them. A potential mechanism that averts cancer is an "over-crowding" gene, p16, which prevents cell division once a group of cells reaches a certain size. The combination of p16 and p27 in naked mole rats cells is a double barrier to cell proliferation.