Stretch marks and weight changes: why they also appear when you lose weight

"I lost weight, and stretch marks appeared." If that sounds familiar, you are not alone. It is one of the most puzzling paradoxes: we associate stretch marks with skin that stretches, and yet they can show up just as the skin relaxes. With the arrival of new obesity treatments, this question concerns more and more people. Let's look at it.

Rapid weight gain: the classic mechanism

When weight increases quickly, the skin has to expand faster than it can adapt. The collagen and elastin fibres in the dermis, which give it its strength and elasticity, end up breaking: a scar forms deep in the skin, the stretch mark¹. Red or purple at first, it fades over time.

Rapid weight loss: why it's counter-intuitive

When you lose weight, the skin is less taut. You might therefore expect stretch marks to fade. The opposite often happens, for three reasons.

1. Stretch marks revealed. Many stretch marks "discovered" during weight loss actually formed during previous weight gain. As long as the underlying volume kept them taut, they stayed discreet. When that volume decreases, the skin slackens and wrinkles, and these marks become much more visible.

2. Skin weakened deep down. Years of stretching leave their mark. Skin analyses carried out after massive weight loss show disorganised collagen, degraded elastic fibres and scarred areas, even in skin that looks normal^2,3. This skin has lost part of its ability to retract: it slackens instead of tightening.

3. The tension paradox. This is the most surprising point. Fibroblasts, the cells of the dermis that produce collagen, need a certain amount of mechanical tension to function normally: it is the stretching of their environment that stimulates them to produce collagen⁴. When the skin suddenly relaxes, this stimulation decreases and collagen production slows down. Yet fibroblasts located in stretch marks already behave differently⁵. On top of this, rapid weight loss is sometimes associated with insufficient protein intake, and protein is an essential building block of collagen. The result: the skin repairs itself less well at the very moment it needs it most.

Science has not yet worked everything out. Stretch marks that appear specifically during weight loss are less studied than those linked to weight gain, and these mechanisms remain partly hypothetical. But they explain well what many people observe.

New obesity treatments

Since 15 June 2026, two medicines have been reimbursed at 65% by French national health insurance for certain adults living with obesity: Wegovy (semaglutide) and Mounjaro (tirzepatide). They are reserved for people with a body mass index of 40 or more, or 35 or more with at least one weight-related condition, after nutritional management has failed; the first prescription must come from specialist doctors⁶.

These treatments enable significant and sometimes rapid weight loss. There has been a lot of talk about their visible effects on the skin, such as sagging of the face or body. Researchers are asking whether these changes are solely due to rapid weight loss, or also to effects of the medicine on the fatty tissue of the skin, on fibroblasts and on oxidative stress. The question has not been settled⁷. To date, no study has looked specifically at stretch marks in people receiving these treatments.

How to support your skin through weight changes

• Aim for gradual change where possible, together with your doctor or dietitian: the skin adapts better to slow changes.
• Make sure you get enough protein and eat a varied diet, which gives the skin what it needs to make collagen.
• Moisturise and massage the skin every day, especially the belly, hips, thighs, arms and chest.
• Watch for red or purple marks: this is the stage when the skin is most receptive to care⁸.

During weight gain, the KOUAGA prevention cream supports skin as it stretches. If recent stretch marks appear, the fading cream is dedicated to that stage. To understand the difference between the two stages, read our article Red or white stretch marks: what's the difference?

Sources

1. Al-Himdani S, Ud-Din S, Gilmore S, Bayat A. Striae distensae: a comprehensive review and evidence-based evaluation of prophylaxis and treatment. Br J Dermatol. 2014;170(3):527-547.
2. Light D, Arvanitis GM, Abramson D, Glasberg SB. Effect of weight loss after bariatric surgery on skin and the extracellular matrix. Plast Reconstr Surg. 2010;125(1):343-351.
3. Orpheu SC, Coltro PS, Scopel GP, et al. Collagen and elastic content of abdominal skin after surgical weight loss. Obes Surg. 2010;20(4):480-486.
4. Varani J, Dame MK, Rittie L, et al. Decreased collagen production in chronologically aged skin: roles of age-dependent alteration in fibroblast function and defective mechanical stimulation. Am J Pathol. 2006;168(6):1861-1868.
5. Viennet C, Bride J, Armbruster V, et al. Contractile forces generated by striae distensae fibroblasts embedded in collagen lattices. Arch Dermatol Res. 2005;297(1):10-17.
6. Assurance Maladie (French national health insurance). Obesity: new medicines may be covered under strict conditions. ameli.fr, June 2026.
7. GLP-1RA and the possible skin aging. Review, 2025. PubMed Central PMC12370548.
8. Ud-Din S, McGeorge D, Bayat A. Topical management of striae distensae (stretch marks): prevention and therapy of striae rubrae and albae. J Eur Acad Dermatol Venereol. 2016;30(2):211-222.