A sacral dimple is a small, usually shallow indentation in the small of the back, just above or within the crease of the buttocks.
About 3 to 8 percent of the population has a sacral dimple. A very small percentage of people with a sacral dimple can have spinal abnormalities.
In most cases, a sacral dimple causes no problems and isn’t associated with any health risks.
The only symptom of a sacral dimple is a generally shallow depression near the end of the tailbone and the top of the buttocks. Most sacral dimples are harmless and don’t need any medical intervention.
Sacral dimple vs. pilonidal cyst
Sacral dimples can be confused with pilonidal cysts because they generally occur in the same area of the body, near the tailbone and just above the buttocks. A pilonidal cyst is a collection of fluid, hair, and debris that forms within a sac. If it becomes infected, it can become swollen and cause pain. Sometimes pus and blood will ooze from the cyst.
A sacral dimple is something you’re born with and a pilonidal cyst is something that develops after birth. Anyone can develop a pilonidal cyst, but it’s most common in young men. Coarse body hair, which can grow inward, along with excessive sweat can produce the right environment for infection.
Scientists aren’t exactly sure what causes a sacral dimple. It’s a congenital condition, which means a person is born with it. It forms for unknown reasons during fetal development. There are no risk factors for developing a sacral dimple.
A sacral dimple is visually evident to doctors during a newborn’s physical exam. If a sacral dimple has no unusual characteristics, it’s called a simple sacral dimple. There’s a high probability that it will have no effect on a person’s health. Because of this, doctors generally don’t recommend any action.
In rare cases, a sacral dimple can indicate an underlying spinal cord defect, such as spina bifida occulta and tethered cord syndrome.
Spina bifida occulta occurs when the spine doesn’t fully close around the spinal cord. Tethered cord syndrome is a condition in which part of the spinal cord attaches to tissue, limiting its movement.
A sacral dimple should be evaluated with an ultrasound or MRI if it’s:
- larger than 5 millimeters in diameter
- accompanied by other “dimples”
- 2.5 centimeters or more above the opening of the anus
- marked by a tuft of hair, skin discoloration or birthmark, or skin tag (a little piece of extra skin)
- deep, meaning that there appears to be a hole inside the dimple that you cannot see the bottom of
In one study published in the journal Archives of Disease in Childhood, sacral dimples with these features were six times more likely to be associated with spinal problems than simple sacral dimples. Learn more about spinal defects and how they’re treated.
There is no treatment for a sacral dimple. Sometimes the “dimple,” or pit in the skin, can collect dirt, fecal matter, and sweat. That increases the risk for infection or irritation. Keeping the area clean will reduce that risk. If you have a baby with a sacral dimple, using a diaper rash cream over the dimple can help keep stool out of the pitted area.
If a person with a sacral dimple has any symptoms of spinal cord problems, like muscle weakness or numbness in the legs, or loss of control of the bladder or bowels, it’s important to see a neurologist for evaluation. While uncommon, surgery to correct an improperly closed spinal cord may be recommended.
Sacral dimples are common and unproblematic in the vast majority of cases. Rarely, they can be indicative of underlying spinal defects. Even when those defects occur, they are usually mild and produce no symptoms. Most people with sacral dimples live normal, healthy lives. The dimple has no effect on their movement or lifestyle.