Skinny guinea pigs come from a breed that is mostly hairless. Skinny guinea pigs usually have sparse hair on their faces, legs and feet, but most of their body lacks the fur that covers other members of their species. The related Baldwin breed is completely hairless.
Skinny and Baldwin guinea pigs require extra care due to their lack of protective hair. In the winter, skinny guinea pigs appreciate a warm environment, and can even benefit from small animal garments such as sweaters. In the summer, they should be kept out of direct sunlight to avoid sunburn and the risk of skin cancer.