A pilonidal dimple is a small pit or hollow area (sinus) in the area at the very top of the crease between the buttocks (sacral area).

Most pilonidal dimples are harmless pits ot small depressions that are present from birth. There may be increased hairiness around the area.

The pilonidal dimple may also be a deep tract, rather than a shallow depression, leading to a hollow space (sinus) that may contain hair. These can become infected and drain. On rare occasions, the sinus may extend into the spinal cord.

During adolescence, the dimple or tract may become infected, forming what is called a pilonidal abscess. It is also called a pilonidal cyst, although a true cyst may not be present. These may require surgical drainage or total removal to prevent reinfection.

• Congenital pilonidal dimple
• Congenital dermal sinus (of which the dimple is the mildest form)

Keep pilonidal dimples clean and free of debris during regular bathing. Report any drainage of fluid from the dimple, either clear or containing pus, to your health care provider.