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Nick Jonas was diagnosed with type 1 diabetes at age 13 and has spent two decades describing the months before diagnosis: thirst, weight loss, exhaustion, the symptoms everyone knows to look for. Most adults with type 2 disease do not present that way.
They present with a rash, a nail change, a wound that will not close, or a neck that someone told them to scrub harder.
Skin findings are among the earliest visible signs of insulin resistance and hyperglycemia, and they are visible to any clinician in any exam room.
The problem is not access. The problem is recognition.
Roughly one in five to one in three adults with diabetes in the United States remains undiagnosed depending on the survey, and the skin has often been signaling for years.
Five mistakes primary care teams make with diabetic skin
1. Reading acanthosis nigricans as poor hygiene.
Velvety, hyperpigmented thickening of the posterior neck, axillae, and knuckles is a cutaneous marker of hyperinsulinemia.
Insulin at high concentrations stimulates keratinocyte and fibroblast proliferation through insulin-like growth factor receptors. In adolescents and young adults, acanthosis nigricans correlates with fasting insulin, BMI, and progression to type 2 diabetes. Patients frequently arrive having been told the discoloration is dirt, and some have scrubbed the area raw.
>Practical tip: any patient with new acanthosis nigricans gets a fasting glucose or A1c, and a lipid panel. In an adult with rapid onset, weight loss, and mucosal involvement, consider internal malignancy (this is rare, but the pattern is distinct).
2. Missing necrobiosis lipoidica.
Necrobiosis lipoidica presents as yellow-brown, waxy, atrophic plaques with telangiectasias, almost always on the shins.
It affects fewer than one percent of people with diabetes, but most patients who develop it either have diabetes or will develop it. The lesions are frequently mistaken for old bruises, stasis dermatitis, or trauma. About a third ulcerate.
>Practical tip: a shin plaque that looks "burned" or waxy with visible vessels through thinned skin should prompt glucose testing and dermatology referral. Do not biopsy the center; ulceration risk is high and healing is poor.
3. Treating recurrent candidal intertrigo without asking about glucose.
Recurrent intertrigo, vulvovaginal candidiasis, balanitis, or oral thrush in a non-immunosuppressed adult is a hyperglycemia screen until proven otherwise. Glucose in sweat and urine feeds yeast.
The pattern is now more common: SGLT2 inhibitors cause glycosuria by design, and genital mycotic infections are their most common adverse effect, with a rare but documented risk of Fournier gangrene carried in the FDA label.
>Practical tip: on the third antifungal prescription, check the A1c and review the medication list. For patients on SGLT2 inhibitors, counsel on hygiene and early reporting of genital pain or swelling.
4. Skipping the foot exam.
Diabetic foot ulcers precede most nontraumatic lower-limb amputations, and the annual incidence of ulceration in people with diabetes runs around two percent, with lifetime risk estimated at 19 to 34 percent.
Recurrence after healing is roughly 40 percent within one year. The ADA recommends a comprehensive foot examination at least annually, and at every visit for patients with prior ulceration or neuropathy. Documentation rates in primary care remain low.
>Practical tip: shoes and socks off. Inspect between toes, check for callus over pressure points, test with a 10 g monofilament, palpate pulses. A callus with hemorrhage inside it is a pre-ulcer.
5. Attributing generalized pruritus and xerosis to age.
Hyperglycemia impairs the skin barrier and drives autonomic dysfunction, reducing sweat and sebum. Diffuse xerosis with pruritus, particularly on the lower legs, is common in poorly controlled diabetes.
In an older patient the reflex is to prescribe emollients and move on. Emollients help. They do not replace the glucose check, and they will not address the neuropathic component when it is present.
>Practical tip: itch without a rash in a patient over 50 warrants a basic metabolic screen, including glucose, renal function, liver enzymes, thyroid, and a CBC.
Why this matters
Diabetes causes microvascular and macrovascular damage silently for years before diagnosis.
Skin is the one organ where that damage is visible without imaging or labs.
A clinician who recognizes acanthosis nigricans in a 16-year-old or necrobiosis in a 40-year-old has an opportunity to intervene before retinopathy, nephropathy, and neuropathy are established.
This is the highest-yield screening exam in medicine, and it costs nothing.
Practical reset checklist
Acanthosis nigricans, any age: A1c or fasting glucose, lipid panel
Waxy atrophic shin plaque: glucose testing, dermatology referral, no central biopsy
Third antifungal prescription in a year: A1c, medication review for SGLT2 inhibitors
Every diabetic patient: annual documented foot exam with monofilament
Itch without rash over 50: metabolic screen before the emollient refill
Poorly healing wound anywhere: glucose testing
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A companion guide for the primary care team diagnosing diabetes: everything you need to know about:
What you are screening for
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Who to screen and how
Six skin signals and what to do with each
The two-minute foot exam
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Look at the neck. Look at the shins. Take the shoes off.
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