Furuncle is a skin infection that infects the hair follicles and the skin tissues. Furuncle or boils are generally caused by a bacteria Staphylococcus aureus. Furuncle may also be caused by other types of bacteria and fungus that is usually found on the skin’s surface. Any damage to the hair follicle gives access to the bacteria to enter the tissues of the follicle and the underlying tissues.Furuncle occurs in the hair follicles in any part of the body. However, they are mostly seen on the face, neck, buttocks, armpits and thighs. At first, the boil may appear tender, swollen, reddish area on the skin. Later, it turns into a water-filled bump or cyst.