Sacral dimples are normal. These small indentations near the base of the spine, just above the buttocks crease, appear in roughly 2% to 7% of newborns. The vast majority are harmless and never cause any problems. That said, certain features can distinguish a completely benign dimple from one that deserves a closer look.
What a Simple Sacral Dimple Looks Like
A “simple” sacral dimple has a very specific profile. It’s a single, shallow indent sitting right on the midline of the lower back, less than 5 mm across (about the size of a pencil eraser), and located within 2.5 cm of the anus. The skin around it looks completely normal, with no unusual hair growth, no birthmarks, no skin tags, and no drainage. If your baby’s dimple fits this description, the risk of any underlying spinal issue is extremely low. A large meta-analysis published in JAMA Network Open found that only about 0.6% of infants with a simple sacral dimple had an underlying spinal abnormality.
Simple sacral dimples form during early fetal development when the skin layers fold inward slightly over the tailbone area. They’re essentially a cosmetic variation, similar to a chin dimple. They don’t close over time, but they also don’t grow or change. Most parents notice them during diaper changes or bath time, and pediatricians routinely check for them during newborn exams.
Features That Make a Dimple Atypical
Not all sacral dimples are simple. An “atypical” dimple raises more concern and typically has one or more of these characteristics:
- Size or depth: Larger than 5 mm, unusually deep, or you can’t see the bottom of it.
- Location: Positioned higher up on the back, far from the anus, or off to one side rather than centered on the midline.
- Multiple dimples: More than one indent in the area.
- Nearby skin changes: A tuft of hair growing around the dimple, a red or purple birthmark (hemangioma), skin tags, a fatty lump under the skin, unusual pigmentation, or a crooked buttocks crease.
- Drainage: Any fluid leaking from the dimple.
When a dimple has atypical features, the chance of an underlying spinal abnormality jumps to about 8.8%, roughly 15 times higher than with a simple dimple. That’s still a minority of cases, but it’s high enough that doctors will want imaging to rule out problems beneath the skin.
What Doctors Are Looking For
The main concern with an atypical sacral dimple is a group of conditions collectively called occult spinal dysraphism. “Occult” means hidden, and these are structural problems in the lower spinal cord or surrounding tissues that aren’t visible from the outside. The most well-known of these is tethered spinal cord, where the spinal cord is anchored too tightly at the base of the spine instead of hanging freely within the spinal canal.
A tethered cord may not cause symptoms right away. As a child grows, the cord gets stretched, and that tension can gradually lead to lower back pain, weakness or numbness in the legs and feet, trouble walking, and loss of bladder or bowel control. These symptoms sometimes don’t appear until a child is walking or even older, which is why catching the condition early matters.
How Sacral Dimples Are Evaluated
If your baby’s pediatrician flags a sacral dimple as atypical, the first step is usually a spinal ultrasound. This painless, radiation-free scan works well in newborns and young infants because their spinal bones haven’t fully hardened yet, giving the ultrasound a clear window to see the spinal cord underneath. It’s the same technology used during pregnancy, and your baby won’t feel a thing.
There’s a time limit on ultrasound’s usefulness, though. As the vertebrae calcify over the first few months of life, the bony spine blocks the ultrasound waves. If a baby is older or if the ultrasound results are unclear, an MRI provides a more detailed picture. MRI doesn’t use radiation either, but it does require the baby to stay very still, which sometimes means light sedation.
For a simple sacral dimple with no other concerning features, most guidelines don’t recommend any imaging at all. A visual exam by the pediatrician is enough.
Living With a Sacral Dimple
A simple sacral dimple requires no treatment, no monitoring beyond routine checkups, and no restrictions on activity. It stays the same size relative to the body as your child grows. You don’t need to clean it any differently than surrounding skin, and it won’t become infected under normal circumstances. Many adults have sacral dimples they’ve never noticed or thought twice about.
If imaging does reveal an underlying issue like a tethered cord, treatment is surgical and typically very effective when caught early, before symptoms develop. But for the overwhelming majority of babies with a small, shallow, midline dimple and no other skin changes, this scenario simply doesn’t apply. The dimple is a minor anatomical variation, nothing more.