Doctors urge checks for crusty brown skin patches and other subtle signs of undiagnosed diabetes

Doctors are urging people to see a GP if they notice subtle symptoms such as crusty brown skin patches, blurred vision, recurrent thrush or tingling in the hands and feet, warning that such signs can indicate undiagnosed type 2 diabetes and lead to serious complications if missed.

The call follows research published in The Lancet last week that found nearly a quarter of diabetes cases in the United Kingdom go undetected. Researchers from the University of Washington estimated about 4.6 million people in the UK have a diagnosis of diabetes while as many as 1.5 million more may be living with the condition without knowing it.

Most of the undiagnosed cases are believed to be type 2 diabetes, which accounts for roughly 90% of diagnoses and is commonly linked to factors including a sedentary lifestyle and poor diet. Type 2 diabetes develops when the body either does not produce enough insulin or becomes resistant to it. Insulin controls blood glucose; without adequate insulin action, high glucose levels can damage blood vessels and organs. By contrast, type 1 diabetes is an autoimmune condition in which the body destroys insulin-producing cells and is typically diagnosed earlier in life.

"The trouble for many patients with type 2 diabetes is that the symptoms come on slowly and become part of everyday life," said Professor Andrew Hattersley of the University of Exeter. He added that common symptoms are often dismissed as normal ageing and that early treatment is crucial to preventing long-term consequences such as heart disease, which is twice as likely in patients with unmanaged diabetes.

Clinicians commonly advise watching for the "four Ts": excessive thirst, unexplained weight loss, fatigue and frequent urination. But experts highlight a range of less well known warning signs. Dr Louise Gow, head of optometry and low vision at the Royal National Institute of Blind People, said fluctuations in vision throughout the day, such as blurriness around mealtimes or prescriptions that suddenly become inaccurate, can be a sign of diabetes and warrant testing.

Dr David Strain, an expert in cardiometabolic health at the University of Exeter medical school, said recurrent infections — especially three or more episodes of thrush in a year — slow-healing cuts and tingling or numbness in the hands and feet are additional red flags. He pointed to crusty, brownish patches of skin, particularly in the armpits or on the neck, known medically as acanthosis nigricans. These patches are darker, thicker and sometimes slightly velvety when high insulin levels cause skin cells to multiply more rapidly. "While these patches are usually harmless, if they appear alongside other symptoms, it is a red flag," Dr Strain said. He noted they are particularly common in Black and Asian people and can be mistaken for eczema or dirt.

Clinicians and patient groups warned that delays in diagnosis and management carry measurable risks. A 2022 study in the BMJ found that failing to diagnose and manage diabetes increases the risk of dying from any cause by about 13%. A 2013 study reported a 73% increased risk of developing dementia among people diagnosed with diabetes. Diabetes UK estimates the condition contributes to about 180 amputations in the UK each week, though many such outcomes can be prevented with timely care.

Personal accounts underscore the potential consequences of missed diagnosis. Mark McGovern, a 47-year-old gardener, said he had experienced thirst, fatigue, frequent urination and pins-and-needles in his feet that he attributed to ageing. In 2016 he suffered a stroke while driving and was later told the event was caused by undiagnosed type 2 diabetes. He said the stroke has had long-term effects on his ability to work and his daily life.

Other patients have found diabetes by chance. Ken Heard, 64, a college tutor with a healthy body mass index, said he only discovered his type 2 diabetes after seeing a pharmacy poster offering checks. Veteran marathon runner Tony Pidgeon, 57, said he was surprised to be diagnosed despite a long history of activity and a healthy weight; he later took part in a University of Oxford trial testing a low-calorie, low-carbohydrate diet and said the regimen helped him control his blood sugar.

Health services offer routes to detection and monitoring. The NHS provides free health checks via GP services for people aged 40 and over to screen for conditions including type 2 diabetes, high blood pressure and heart disease. Experts advise that patients who suspect they may have diabetes ask their GP for an HbA1c blood test, which measures average blood glucose over the previous two to three months and is used to diagnose and monitor diabetes.

Treatment and monitoring options aim to reduce blood glucose and prevent complications. Clinicians commonly recommend weight loss, a diet rich in vegetables and whole grains, and regular physical activity; research shows losing 5 to 10% of body weight can substantially improve blood sugar control and in some cases lead to remission. When lifestyle measures are insufficient, medications such as metformin are typically prescribed, with other agents or insulin added as needed. Ongoing monitoring often includes regular blood tests, eye checks and foot examinations to detect complications early.

Experts highlighted particular concern about underdiagnosis among younger adults. The Lancet research found people under 35 were least likely to be diagnosed, with only about one in five aware of their condition. Professor Hattersley said younger people are less likely to visit a GP and that there remains a perception that diabetes primarily affects older people, which can delay testing.

Commenting on the research, Nikki Joule, policy manager at Diabetes UK, said underdiagnosis of type 2 diabetes remains a major challenge in the UK, particularly among young people, and that improving diagnosis and treatment is essential given the high prevalence of diabetes and prediabetes.

Clinicians advised that anyone noticing the described symptoms, including painless skin changes, recurrent infections, vision changes or unexplained fatigue, should consult a GP and request appropriate testing rather than assuming the signs are merely the result of ageing.