A “butt chin,” formally called a cleft chin, is a small vertical indentation in the center of your chin. It forms because the two halves of your jawbone didn’t fully merge together during fetal development, leaving a slight gap that shows through the skin. It’s a completely normal anatomical variation, not a defect, and somewhere between 5% and 25% of people have one depending on ethnic background.
How a Cleft Chin Forms Before Birth
Your lower jaw starts as two separate pieces. During the fourth and fifth weeks of embryonic development, these two halves (called mandibular processes) gradually enlarge and begin merging together at the midline. The spot where they meet becomes your chin. Between the fifth and eighth weeks, cartilage rods form within each half of the jaw, providing scaffolding for the bone that will eventually harden around them.
When this merger is complete, the chin surface is smooth. When it’s partial or incomplete, a visible indentation remains right at the midline. That indentation is your cleft chin. It’s not that something went wrong. It’s simply a variation in how thoroughly those two halves knit together, similar to how some people have attached earlobes and others have detached ones.
The Role of Your Chin Muscle
Bone isn’t the only factor. The mentalis muscle, a small muscle that sits right on the front of your chin, plays a significant role in how deep or visible the cleft looks. This muscle originates from the front surface of your jawbone and inserts directly into the skin of your chin through multiple fiber bundles. It has medial fibers that descend in a dome shape, lateral fibers that angle outward, and upper fibers that connect to the muscle around your mouth.
Because these fibers attach to the skin itself, every time the muscle contracts (when you pout, push your lower lip up, or tense your chin), it pulls the skin inward at the attachment points. If the medial fibers on each side of the midline don’t overlap or connect across the gap, the cleft becomes more pronounced. This is why some people notice their chin dimple looks deeper when they make certain facial expressions but flatter when their face is relaxed.
Genetics and Inheritance
Cleft chins run in families, and for decades genetics textbooks used them as a classic example of a dominant trait. The simplified version: if you carry even one copy of the allele (gene variant) associated with a cleft chin, you’ll likely have one. Two parents without cleft chins are less likely to produce a child with one, though it can still happen if both carry a recessive copy of the trait.
The reality is more nuanced than a single on-off gene. The depth and visibility of the cleft varies widely, which suggests multiple genes and possibly environmental factors during fetal development influence the final result. You might have a barely noticeable crease while a sibling has a deep, clearly defined cleft. Still, the basic inheritance pattern holds: if one or both of your parents have a cleft chin, your odds of having one go up substantially.
Is a Cleft Chin a Health Concern?
A cleft chin on its own is purely cosmetic. It’s not associated with any medical condition or syndrome. The underlying bone variation is minor and doesn’t affect jaw function, bite alignment, or dental health. It’s worth noting that true midline clefts of the mandible (where the jawbone is significantly split) are an entirely different and extremely rare condition. A chin dimple is not a cleft in that clinical sense.
Options If You Want to Change It
Some people love their cleft chin. Others would prefer a smoother profile. If you fall into the second group, several cosmetic options exist, ranging from quick office visits to surgery.
- Dermal fillers: A synthetic filler is injected directly into the cleft to smooth it out. The procedure takes minutes and results last six to twelve months before the filler is naturally absorbed.
- Botox: Injections can relax the chin muscle so it stops pulling the skin inward, reducing the cleft’s appearance. Effects last a few months. Botox is often combined with fillers for a more complete result.
- Fat grafting: Fat is removed from another area of your body (typically the abdomen), processed, and injected into the chin. Results are longer lasting than synthetic fillers, though the procedure may slightly increase overall chin size.
- Genioplasty: Chin surgery involves reshaping the jawbone or repositioning the muscle attachments. Results are usually permanent, but recovery takes several weeks to months, and the procedure requires anesthesia. Chin implants can also be placed to create a rounder chin shape.
For fillers and Botox, there’s minimal downtime. For surgical options, expect a longer commitment: the American Society of Plastic Surgeons notes that final results from genioplasty can take several weeks to months to fully appear. The right choice depends on how deep your cleft is, how permanent you want the change to be, and your comfort level with the procedure involved.