Hello, I'm Dr. Yoosuk Chung, plastic surgeon at TheLine Plastic Surgery.
Is it sagging, or was the fat always there?
When the jawline loses definition and sagging tissue (jowls) becomes noticeable, many people aren't sure whether it's from weight gain or from age-related sagging. For a long time, the medical literature explained jowls as resulting from the "mandibular ligament" stretching and loosening with age.
To get straight to the point: this conventional explanation is now being re-examined by detailed anatomical research. A 2023 study that precisely analyzed 49 cadavers using micro-CT found that the mandibular ligament itself does not actually stretch with age. Instead, the subcutaneous connective tissue covering it lengthens, and the fat compartments of the cheek slide downward — and this appears to be the more direct cause of jowl sagging.
Why did this new finding emerge?
Jowl formation results from the interaction between the mandibular septum, the fat compartments below the jaw, and the overlying skin[1]. A classic 2008 study described jawline aging through roughly three patterns: fat atrophy, displacement of fat compartments, and dehiscence (separation) of the mandibular septum[1].
The 2023 study went a step further, re-examining exactly what structure actually lengthens. Using standardized layered dissection, sheet plastination, and micro-CT on 49 cadavers, the researchers found the somewhat unexpected result that the mandibular ligament — the deep attachment directly connecting bone to soft tissue — does not stretch with age[2]. Instead, they found that the thin, elastic subcutaneous connective tissue overlying the ligament — which normally allows the jawbone to move freely — lengthens with age, resulting in redundant slack in the skin and subcutaneous tissue[2].
Think of it this way: the older explanation was like a fence post (the ligament) itself bending or stretching. The newer research suggests the post stays the same — but the netting wrapped around it (the connective tissue) stretches, letting what's inside (the fat) spill through the gaps.
Much like how skin and the SMAS layer beneath it age at different rates ("Why Doesn't My Firming Cream Work?: The part of Sagging Skincare Can't Reach"), jowl sagging also turns out to be a mix of changes in two distinct structures — the ligament and the connective tissue above it. Facial sagging often isn't the result of a single cause, but rather several layers and structures changing in their own ways and overlapping.
So what about the fat compartment theory?
Some researchers view the movement of fat compartments as a more significant factor in jowl formation than the mandibular ligament itself. As the cheek's fat compartments and the tissue that once supported them shift downward with age, this is thought to contribute more to jowl formation than ligament laxity alone. Taken together, recent research suggests jowl sagging isn't a problem with the ligament alone — it's closer to a combination of changes in the connective tissue and the downward movement of fat compartments.
In summary, the long-standing explanation that "the ligament stretches, causing the jawline to sag" is now being reconsidered by detailed anatomical research. Current evidence suggests that changes in the connective tissue above the ligament, combined with the downward shift of fat compartments, may be the more direct cause.
Individual variation and things to keep in mind
The timing and degree of jowl sagging can vary between individuals depending on genetic factors, skin thickness, and weight changes.
Jowl sagging often occurs alongside fat accumulation (a "double chin"), so distinguishing between the two typically requires an in-person examination.
The exact mechanism in this area remains an active area of research, and the explanation may continue to be refined as more evidence accumulates.
The studies cited above analyze anatomical structural changes; they are not clinical trials directly testing the effectiveness of any specific procedure.
Three key takeaways
1. Jowl sagging has long been explained as resulting from the mandibular ligament stretching with age[1].
2. A detailed 2023 study of 49 cadavers found the ligament itself does not stretch — rather, the connective tissue above it lengthens and fat compartments slide downward, which appears to be the more direct cause[2].
3. Jowl sagging is best understood not as a problem with the ligament alone, but as a combination of connective tissue changes and fat compartment movement, in line with the latest research.
What's causing your jawline sagging is best confirmed through an in-person consultation with a specialist.
By Dr. Yoosuk Chung (Board-Certified Plastic Surgeon)
--- Sources
1. Marten TJ, Elyassnia D. The Aesthetic Jaw Line: Management of the aging Jowl. Aesthet Surg J. 2008. ScienceDirect
2. Minelli SI, Yang HM, van der Lei B, Mendelson B. The Surgical Anatomy of the Jowl and the Mandibular Ligament Reassessed. Aesthetic Plast Surg. 2023. PubMed 36050569
This article summarizes questions around the causes of jowl sagging based on research published in academic journal. This remains an active area of research; please consult a specialist to confirm your individual condition.