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What Is It?

The least you need to know (Cliff Notes Version):

A Pilonidal (Abscess, Cyst, Sinus, Dimple) is an abscess in the natal cleft (more commonly referred to as your butt crack) that tends to become infected and cause intense pain and drainage. Sometimes a Pilonidal contains hair and sometimes they don't.

A few basic facts:

  • FACT: The term "Pilonidal" technically means "nest of hairs" and much medical literature is devoted to the idea that hair in the buttock cleft is what causes Pilonidal. This is not always true and approximately 50% of sufferers are found to have no hair in their Pilonidal Abscess (most frequently the case in females.) Hair can play a role in Pilonidal Disease, but the real culprit is an expanded/exploded follicle called a "pit" in the midline of the buttock cleft. A Pilonidal cyst is basically an abscess beneath the skin - a boil gone very, very bad. Pilonidal abscess are prone to excruciatingly painful infections and they can expand or "tunnel".
  • FACT: The term "Pilonidal Cyst" is actually incorrect. 99% of all Pilonidals are actually abscesses, not cysts. Use of the word "cyst" has caused a great deal of misinformation about treatments among doctors and patients alike. Pathologists and surgeons on rare occasions find the sac is lined with epidermis, made up of cells from skin, but only cells from the outer layer of skin. That outer layer, which we call epidermis, contains no follicles. Pathologists find epidermis lines the sac only in rare late cases where epidermis has crept into a long-standing abscess in an attempt to heal it. They never find a sac lined with intact skin and follicles, only an occasional sac lined with epidermis. What this means to the patient is that emphasis on surgery to remove the "sac" is ill informed and the focus should be on the root cause of the abscess - the pits in the midline.
  • FACT: While the terms Pilonidal Cyst and Pilonidal Sinus are frequently used interchangeably, they are not technically the same thing. A Pilonidal is an abscess; a pocket of infection below the skin. A sinus is a cavity/passageway that links the abscess with your outer skin. Not everyone who has a Pilonidal abscess has a Pilonidal Sinus; the sinus (and there can be more than one) is a small dimple-like hole, usually below the actual abscess, which allows it to drain.
  • FACT: Pilonidal abscesses usually occur at the top of the "natal cleft" (aka your butt crack). Their usual position is slightly to the left side, with sinus openings traditionally right along the midline (middle) of the cleft. Many people have cysts lower in the cleft or on both sides, it depends on the individual. Severe Pilonidal Disease with multiple tracts/sinuses can extend from the anus all the way to top of the buttock cleft.
  • FACT: The peak incidence of Pilonidal Disease is between 16 and 26 (however, older and younger happens regularly too). We have heard from people in their 50's having their first Pilonidal episode and from parents with children as young as 12. Our experience is that girls see signs earlier at the start of puberty (12 - 14) than boys, who we hear about more in the 16 - 22 age range. It affects males only slightly more than females. It is uncommon (but not unknown) in Asian and Black peoples.
  • FACT: Many babies are born with a "Sacral Dimple"; however, this is not the same as the Pilonidals discussed on this site. Some Sacral Dimples will become infected and turn into Pilonidal abscesses, but most are harmless blind tunnels (which should be checked anyway for possible connections with other problems.)
  • FACT: Pilonidals rarely go away on their own. Most require some form of surgical intervention, although there are cases of "disappearance" after a lancing or antibiotic treatment. Pilonidals can go dormant for years at a time, lulling their owner into a false sense of escape. Every sufferer's Pilonidal experience is uniquely their own - experiences range from regular flare-ups and constant miser to flare-ups that occur randomly with long gap (sometimes years) in between.
  • FACT: Pilonidal abscesses are medically related to a group of diseases known as Follicular Occlusion - meaning blocked hair follicles. At one time it was believed that Pilonidals were all congenital, however, current medical philosophy is that very few of these abscesses are congenital and most are acquired.

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This page last updated: January 17, 2011

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An abnormal closed epithelium-lined cavity in the body, containing liquid or semisolid material.

Sacral Dimple

A small hole located just above or between the buttocks - usually found in babies. The name comes from the sacrum, the bone at the end of the spine, over which the dimples are found. More than 2% of babies may have such dimples; almost all of these are very minor. May be related to Spina Bifidia Occulta and should be checked by a doctor.

Natal Cleft

is the groove or crack between the buttocks that runs from just below the sacrum to the perineum, so named because it forms the visible border between the external rounded protrusions of the Gluteus maximus muscles.

Also referred to as the "Intergluteal Cleft", "Midline", or the more common "butt crack".

Pilonidal Sinus

A sinus is a cavity in any organ or tissue. In the case of Pilonidals, a sinus forms as a chronically infected tract between the Pilonidal Abscess and the skin. Most sinuses are found in the midline as a result of exploded follicles, although in some severe cases, sinuses can form along the sides and top of the buttocks. It is important that sinuses be excised surgically or layed open to heal because they provide access below the skin for foreign bodies such as hair, clothing lint and other debris that instigate infection.

Pilonidal Cyst/Abscess

A special kind of abscess that occurs in the cleft between the buttocks. It can be extremely painful and generally requires surgical intervention.


An abscess is an enclosed collection of liquefied tissue, known as pus, somewhere in the body. It is the result of the body's defensive reaction to foreign material.