A pilonidal cyst (intergluteal pilonidal disease) is a skin condition caused by local inflammation of the superior midline gluteal cleft, which may progress to a local abscess or fistula. It is currently hypothesized to be an acquired condition with local penetration of hair follicles and debris in stretched intergluteal pores. Affected individuals – typically obese, sedentary men with excessive body hair and a deep gluteal cleft – may be asymptomatic or present with mild local symptoms such as local oozing or erythema; however, abscesses can also cause severe pain. Pilonidal cysts are diagnosed based on patient history and clinical examination. To treat the condition, radical resection with secondary wound healing is usually necessary. Asymptomatic patients can be treated conservatively.
Epidemiological data refers to the US, unless otherwise specified.
The exact mechanism is unknown, however, the current prevailing hypothesis is that pilonidal disease is an acquired condition.
- Sitting or bending cause hair follicles, in vulnerable skin within a deep natal cleft, to stretch and break → formation of an open pore or pit. These open pores either collect debris or broken hair roots (from the head, back or buttocks).
- Movement causes negative pressure (e.g., “suction effect”) and further penetration of hair into local subcutaneous tissue → formation of a pilonidal sinus 
- These collections trigger local tissue inflammation within the pilonidal sinus → acute infection (abscess) or fistulae 
- Possible history of trauma or surgery for pilonidal cyst
- May be asymptomatic
- Simple sinus tract opening in sacrococcygeal region, ∼ 5 cm from the anal verge
- Acute inflammation (e.g., abscess)
- Chronic inflammation
The differential diagnoses listed here are not exhaustive.
- Asymptomatic patients
- Postsurgical care of symptomatic patients
- Improved local hygiene
- Local hair control (e.g., laser epilation) 
- Observation for signs of infection
- Indication: symptomatic patients
- Acute pilonidal cyst: incision and drainage, with secondary wound closure
- Chronic or recurrent pilonidal sinus: surgical resection