A double chin is four things. Only one of them dissolves.

If the pinch test finds a soft pad and the neck skin is firm, weight loss is the free treatment and the pad shrinks with the rest of you, though the neck is often the last place to give it up. If the recline test says slack, weight loss makes the double chin looser, not smaller; if the profile says a short chin, no weight will change the angle; and the deep fat between the digastric muscles is stubborn at every weight. The GLP-1 medicines have shown what fast loss does to an older neck: the fat leaves, the envelope stays. Lose at a pace the skin can follow, keep the weight off, and do the four tests again before deciding what is left.

Deoxycholic acid is the better-evidenced and the stronger of the two: two placebo-controlled trials of over a thousand people, 66–70% improved against 19–22% on placebo, most within two to four sessions, response held at three years. Its price is one to two weeks of swelling and numbness after every session, a 4% rate of temporary weakness of the nerve to the lower lip, and a course that costs as much as liposuction. Cryolipolysis removes about 2–3 mm of fat per cycle in a meta-analysis of 206 patients, with an easier fortnight and a rare but permanent risk of the fat enlarging instead. For a small pad, either; for a large one, the injection or a morning of liposuction; for any of them, a firm neck and a decent chin first, because neither touches anything but fat.

Adults do not make new fat cells in any number, so the cells destroyed by deoxycholic acid, killed by cold or removed by a cannula are gone: in the REFINE follow-up of patients who had responded, 82.4% of those given the drug still held their response at three years against 65% of placebo responders, and liposuction series report durable contour. What is not permanent is everything else — the remaining fat cells enlarge if weight rises, the deep fat and the glands descend with age, the skin loosens and the platysma slackens — so a neck treated for fat at forty can look full again at fifty-five for reasons that no longer answer to a fat treatment. The four tests, repeated, tell you which problem has returned.

Rapid weight loss empties the fat above and below the platysma within months, and skin that has lost recoil with age or sun does not retract to match; clinicians treating GLP-1 patients describe exactly this neck alongside a hollowed midface. The double chin has changed type from fat to slack, and the tests confirm it: the fullness vanishes lying back and hangs looking down. Nothing that removes fat helps now. Mild slack in younger skin retracts over a year and tightens further with focused ultrasound; moderate slack is the territory of subdermal plasma with light liposuction; a neck that hangs is a neck lift, and the sooner the surgeon sees it before anyone injects, the simpler the operation.

The fat under the chin is not a muscle, the platysma is a thin sheet that lifts nothing, and the skin does not tighten from movement. The case report that examined jaw-exercise devices found the masticatory muscles they train have no action on submental fat or elasticity, and the American Association of Orthodontists finds no evidence that pressing the tongue to the palate reshapes the jaw once growth has finished. Holding the head up and the chin forward makes any neck look better in a mirror and in a photograph, which is worth knowing for photographs; it is not a treatment, and the clinic that sells one is selling posture.

The angle under the chin is geometry: the longer the line from chin to hyoid, the sharper it is, and a chin that sits behind a line dropped from the lower lip shortens that line however lean the neck. This is the double chin that runs in families and appears in the leanest relative, and it is the one most fat clinics never mention because they do not sell the fix. Chin filler — a firm gel on the bone, corrected retrusion in 56% against 28% of untreated controls in a 192-person randomised trial — shows you the profile in an afternoon; a chin implant or a sliding genioplasty makes it permanent, and surgeons pair either with liposuction because the two together sharpen the angle more than either alone. A profile photograph with the head level is the test.

"Start with the least invasive option" is right for the double chin the self-check calls fat above the muscle in a firm neck, where the injection or the applicator has placebo-controlled or meta-analysis evidence and may be the whole answer. It is wrong for the neck that reclines away, will not pinch, or cords when you clench, because those necks were always going to need a surgeon and the surgeons now report what the detour costs: in 180 consecutive neck lifts, 68% of patients had had earlier neck treatments, surgical or not; after non-surgical ones the tissue planes were fibrosed and the fat unpredictable, every previously treated neck took longer to operate on, and nearly all were left with contour irregularities. A surgical consultation is not a commitment to surgery; it is the opinion that tells you whether the syringe would help or hurt.

Deoxycholic acid swells for one to two weeks after each session and the fat clears over six to eight, so a course of two to four sessions plays out over four months; cryolipolysis is judged at eight to twelve weeks per cycle. Liposuction is swollen for weeks in a compression garment and final at three to six months. Focused ultrasound, radiofrequency and the muscle-stimulation device remodel over three months, which is when the studies measured them. Chin filler shows the profile immediately and settles at two weeks. A neck lift is bruised and tight for two to three weeks, presentable once that has passed, and final at six to twelve months as the swelling under the chin clears. Photograph in profile with the head level before anything, and again at the interval the treatment deserves.

The ladder in euros: weight lost slowly (free, the fat type only) → sunscreen and a retinoid on the neck (€10–30 a month, the skin) → chin filler for the short chin (€400–800, a year or two) → deoxycholic acid injections (€500–900 a session, two to four sessions, placebo-controlled) or cryolipolysis (€600–1,200 a cycle, one to two) → focused ultrasound or radiofrequency for mild slack (€500–1,200) → submental liposuction (€2,500–5,000, once) → subdermal plasma with liposuction (€4,000–8,000) → a chin implant or genioplasty (€3,000–8,000) → a neck lift (€8,000–18,000, a decade). Unlicensed fat dissolvers, chin straps and jaw trainers sit under the ladder; the profile photograph decides which rung is yours.

The pivotal trials printed the rates: marginal mandibular nerve paresis — the nerve to the lower lip, giving a crooked smile — in 4.3% of treated patients against 0.4% on placebo, all temporary and resolving without sequelae; dysphagia in 1.9% for a median of three days; and injection-site swelling, pain, numbness and firmness in most patients for one to two weeks after every session (REFINE-1; pooled REFINE analysis; prescribing safety profile). Injected too superficially it ulcerates skin; injected outside the marked grid it can reach the nerve or the thyroid cartilage. The subtler harm is the wrong neck: in a lax or subplatysmal double chin the drug removes what was filling the envelope and leaves the slack or the deep fullness in plain view, which the phase 3b trial's "laxity unchanged or improved" finding does not contradict, because those patients were selected for firm skin. Pinch, recline and profile before the grid is drawn.

Paradoxical adipose hyperplasia is the complication that makes cryolipolysis a decision rather than a purchase: two to four months after treatment, the frozen fat grows back larger and firmer in the shape of the applicator, does not resolve on its own, and is corrected with liposuction or excision. A 2025 systematic review and meta-analysis of 28 studies in 13,078 patients put the pooled incidence at 0.22% — about 1 in 455 — against the manufacturer's reported 0.033%, with men overrepresented (16 of the 27 cases whose sex was reported, while men were 13% of the patients in those studies) and first-generation applicators implicated in most (meta-analysis); an eight-centre review of 8,658 cycles found rates of 0.05–0.39% falling by more than 75% with newer applicators (8,658-cycle review); a submental case was corrected with a deep-plane neck lift, its surgeons judging that liposuction would have treated the dense, fibrotic fat poorly (case report). The pivotal submental study recorded no case of it and only passing side effects — prolonged redness in two of 60 people, darker skin in one and a feeling of fullness in the throat in one, all gone within six weeks (pivotal study); a case report describes atypical pain developing after submental treatment (case report). Ask which applicator generation the clinic uses and what happens if the fat grows.

Submental liposuction's complications are rare and serious: the scoping review of published cases lists contour depressions, scar contracture, transient facial-nerve weakness and three cases of necrotising fasciitis, with haematoma and airway compromise the early emergency (scoping review). The neck lift's are counted across 8,648 patients: nerve palsy in 0.2–12% of series, haematoma in 0.2–4%, with scars under the chin and behind the ears and months of numbness (systematic review). The newer caution concerns order: in a series of 180 neck lifts, 68% of patients had had earlier neck treatments, surgical or not; after injections, cold, threads or energy treatments the surgeon found fibrosis, lost planes and unpredictable fat, every previously treated neck took longer to operate on, and nearly all were left with contour irregularities (94% of all 180 needed deep cervicoplasty with subplatysmal work, treated before or not) (ASJ, 2026). For the neck that the self-check says is loose or deep, "non-invasive first" is not the cautious route; a surgical consultation before the first syringe is.

Every device that tightens under the chin does it by controlled injury, and the harms follow the physics. Focused ultrasound aimed too deep or too densely dissolves the superficial fat of a thin neck — the hollowed, stringy look that appears months later — and the marginal mandibular nerve runs superficially along the jaw where the passes go, so a temporarily weak lower lip is a recognised event (meta-analysis). Radiofrequency and needle radiofrequency burn if the settings or the cooling are wrong, and the FDA's alert on radiofrequency microneedling burns and scars is recent (FDA alert). Subdermal helium plasma has a safety communication on burns and subcutaneous emphysema (FDA safety communication). The radiofrequency-and-muscle-stimulation device reported no adverse events in its one study of 33 patients, which its manufacturer funded and designed (MRI study). Ask who holds the handpiece, how many necks a month, and what they do when the neck is thin.