Several mechanisms affect the skin in obesity. Friction and moisture in folds encourage intertrigo, which may be complicated by a yeast infection. High insulin levels can stimulate epidermal cells through IGF-1 growth-factor receptors and be associated with dark thickening in flexures. Inflammation related to excess adipose tissue may contribute to skin disease flares. Blood supply, swelling and other conditions also matter. Appearance alone does not always establish the cause.
A 2026 observational analysis of the US-based TriNetX database associated leg ulcers and lymphoedema with more bacterial cellulitis of the lower leg. Obesity, diabetes, venous insufficiency and athlete's foot were also relevant. Medical-record studies show associations but do not prove a single infection mechanism or predict an individual's outcome. Swollen lower legs and cracked skin between the toes need assessment and treatment of the cause alongside obesity care.
| Skin change | Possible contributing factors | Next steps | Assessed by |
|---|
Dark, velvety patches on the neck and in the armpits | Acanthosis nigricans, often associated with insulin resistance | Glucose metabolism assessment; patches fade after weight loss in some people | doctor, dermatologist |
Redness, burning and weeping in folds | Friction, moisture and possible infection | Drying and loose clothing; antifungal treatment after assessment if a fungal infection is responsible | GP |
Painful lumps and abscesses in armpits and groin | Possible hidradenitis suppurativa, an inflammatory condition associated with obesity and smoking | Dermatological diagnosis, obesity care and help to stop smoking | dermatologist |
Psoriasis responding poorly to treatment | Body weight and adipose inflammation may affect its course | Weight loss may support the response to dermatological treatment | dermatologist |
Hair loss two or three months after rapid weight loss | Possible telogen effluvium, deficiencies, medication effects or other causes | Review of diet, symptoms and necessary tests; decision about continuing medicine | treating doctor |
A skin fold on the abdomen after substantial weight loss | Reduced skin elasticity and changes in collagen and elastin | Assessment of weight stability; consultation for chafing and infections | plastic surgeon |
Dark patches on the neck, or acanthosis nigricans
Acanthosis nigricans causes symmetrical brown thickening with a velvety surface, most often on the neck, in the armpits and groin. It can look like dirt, but scrubbing does not remove it and irritates the skin. A 1992 Archives of Dermatology paper found it in 74% of 34 randomly selected adults at a US obesity clinic; their fasting insulin was higher than in the others. This small clinic sample does not establish prevalence in Poland. A 2023 prospective study of 319 people after sleeve gastrectomy included 141 with acanthosis nigricans. Changes improved in some patients after surgery alongside metabolic improvement; this cannot be assumed for every weight-loss method.
This appearance may justify investigating glucose metabolism but does not diagnose hyperinsulinaemia. Routine fasting insulin testing is not required for obesity-treatment assessment. A dermatologist chooses topical treatment for marked changes. Rapid onset, especially with unintentional weight loss, requires urgent investigation, including for cancer. This also applies to someone who still has obesity.
Painful lumps in the armpits and groin, or hidradenitis suppurativa
Hidradenitis suppurativa is a chronic inflammatory hair-follicle disease causing painful nodules, abscesses and sinus tracts, often in skin folds. It may resemble recurrent boils and needs dermatological diagnosis. A JAMA Dermatology study used Mendelian randomisation, an analysis based on genetic predisposition to higher BMI, and included 4,814 cases and over 1.2 million controls. The odds ratio was 1.20 per BMI unit: 20% greater odds, not a 20% increase in absolute risk. The result supports a causal relationship under the method's assumptions but does not say how much weight loss will change an individual's risk. Additional smoking analyses in that study were inconclusive.
The dermatologist decides about antibiotics, biological treatment or surgery. Weight reduction and smoking cessation may support care but cannot guarantee fewer flares. Reports of improvement with medicines acting on the receptor for the gut hormone GLP-1 come from small studies and case reports. Evidence remains preliminary and does not create a separate indication for these drugs in hidradenitis suppurativa.
Psoriasis in obesity and the effects of weight loss
Obesity is associated with more frequent psoriasis, greater severity and poorer responses to some treatments. A 2008 Italian trial included 61 people with obesity and psoriasis receiving low-dose ciclosporin; some were also randomly assigned a reduced-calorie diet. After 24 weeks, PASI75, an improvement of at least 75% in the psoriasis severity score, was achieved by 66.7% of the diet group and 29.0% of the drug-only group. Mean weight loss in the diet group was 7.0%. In a 2013 Danish trial of 60 people, the intervention involved eight weeks at 800 to 1,000 kcal daily and eight weeks gradually returning to 1,200 kcal. The between-group difference in weight reduction was 15.4 kg. The PASI difference was not statistically significant (P=0.06), while improvement in quality of life measured by DLQI was significant (P=0.02). Such a restrictive diet requires supervision and is not advice for self-treatment.
Weight reduction can complement psoriasis treatment but does not replace it. Doses of some biological medicines depend on body weight, so the dermatologist should know when obesity treatment starts and how it progresses. The treating doctor decides about changes to dermatological medicine.
Hair loss during rapid weight reduction and what to do
Hair loss during treatment may relate to the rate of weight reduction, nutrition, medicine or another cause. One possibility is telogen effluvium: a metabolic change shifts some follicles into a resting phase, with shedding two to three months later. Wegovy information for the 2.4 mg regimen reports hair loss in 2.5% of treated patients and 1.0% on placebo. The frequency at 7.2 mg differs. At 2.4 mg, reports were more frequent after losing at least 20% of body weight; symptoms were usually mild and often resolved while treatment continued. A meta-analysis of 41 papers covering 7,044 bariatric surgery patients reported 47% hair loss, with varying follow-up periods.
A 2026 meta-analysis included 17 studies and 1,091,743 patient exposures, not necessarily that many different people. The estimate for non-scarring alopecia from three cohorts was OR 1.40, meaning 40% higher odds in people using GLP-1 medicines, not a 40% rise in absolute risk. The authors discuss deficiencies after rapid weight loss as a possible contribution; this does not establish each patient's cause. Report marked hair loss to a doctor, who will assess diet, weight-loss rate, tests and continued medication. Improvement may take months. Patchy loss, inflammation, scarring or a severe problem warrants dermatology assessment without waiting six months.
Excess skin after substantial weight loss
Excess skin can remain after losing tens of kilograms. A 2024 histology study compared 80 samples taken during plastic surgery. It described similar collagen loss after weight reduction with and without bariatric surgery, and fewer elastic fibres in abdominal skin after bariatric surgery. It describes tissue structure; it does not show that excess skin depends only on kilograms lost or that treatment type is irrelevant.
An abdominal skin fold can cause chafing, persistent intertrigo and recurrent infections, and interfere with hygiene or movement. Document symptoms, previous treatment and weight changes for a surgical consultation. The centre assesses whether surgery is possible, its funding and the required period of stable weight using the indications and records. A purely cosmetic procedure is a different situation; describing chafing alone does not guarantee NFZ funding.
Injection-site skin and rotating injection sites
In weight-management trials of tirzepatide, injection-site reactions occurred in 8.0% of treated patients and 1.8% on placebo; 91% were mild. These findings do not rule out a severe reaction in an individual. Saxenda information describes injection-site cutaneous amyloidosis with an unknown frequency. A hard lump needs assessment and cannot be diagnosed from a description alone. Inject into the abdomen, thigh or upper arm as directed for the product, changing the site each time and avoiding lumps and affected skin. Increasing pain, spreading redness, discharge or fever needs urgent assessment. Unopened pens are generally stored at 2 to 8°C in a refrigerator, following the leaflet. Six weeks below 30°C after first use applies to multidose Wegovy FlexTouch; other packs may have different rules. Collect needles in a puncture-resistant container and take them to a facility accepting sharps. In Gdańsk, such waste is accepted at municipal selective waste collection points (PSZOK) and sorting centres, among others. A pharmacy with a medicine-return bin does not necessarily accept needles.