Boil is a medical condition that is characterized by pus-filled abscess caused by a localized infection of a hair follicle. They can be caused by foreign particles in the skin, infected sweat glands or ingrown hairs. They begin as warm, reddened areas which eventually become cystic and firm as they fill with pus, eventually resolving without intervention, and can be as large as a golf ball or as small as a pea. Several types of boils exist: furuncle/carbuncle (usually caused by Staph. aureus), nodulocystic acne (caused by infected sebaceous ducts), hidraddenitis suppurativa (caused by inflammation of sweat or sebaceous glands), and pilonidal cyst (only occurs in crease of buttocks; typically after prolonged sitting). Immunocompromised, diabetic or feverish individuals with boils should seek medical advice, as should individuals with boils which persist or spread. On rare occasions, boils may result in systemic infection or sepsis.