Experts urge checks after crusty brown skin patches and other subtle signs point to undiagnosed type 2 diabetes

Doctors and diabetes specialists are urging people to see a doctor if they notice crusty brown skin patches, changes in vision or recurrent infections, after new research found a substantial number of diabetes cases in the UK remain undetected.

A study published last week in The Lancet and conducted by researchers at the University of Washington estimated that nearly a quarter of diabetes cases in the UK are not diagnosed. The researchers said about 4.6 million people in the UK have been diagnosed with diabetes and an estimated 1.5 million people are living with the disease unknowingly, the vast majority with type 2 diabetes.

Clinicians say those skin changes—medically known as acanthosis nigricans—are often harmless but can be an external marker of insulin resistance, the stage when the body struggles to use insulin effectively and which commonly precedes type 2 diabetes. The patches typically appear as darker, thicker, sometimes slightly velvety areas in skin folds such as the armpits or neck and can be mistaken for eczema or dirt.

"These are incredibly common, particularly in Black and Asian people," said Dr. David Strain, an expert in cardiometabolic health at the University of Exeter medical school. "While these patches are usually harmless, if they appear alongside other symptoms, it is a red flag. Catching diabetes early is key to preventing complications."

Doctors warn that the classic signs of diabetes—sometimes summarised as the "four Ts": thirst, thinner, tired and toilet (excessive thirst, unexplained weight loss, fatigue and frequent urination)—are not the only clues. Subtler indicators include fluctuating vision, recurrent thrush or other infections, slow-healing cuts, tingling or numbness in hands and feet and the skin changes described above.

"If patients are experiencing fluctuations in their vision throughout the day—for example, periods of blurriness around mealtimes—this may be a sign of diabetes and they should get tested," said Dr. Louise Gow, head of optometry and low vision at the Royal National Institute of Blind People. She added that it is common for people to return soon after an eye test saying their glasses prescription no longer feels right, which can be caused by blood sugar fluctuations.

Cases of undiagnosed diabetes can have serious consequences. Mark McGovern, a 47-year-old gardener, said he ignored symptoms such as nighttime urination, constant thirst and tingling in his feet until he suddenly developed double vision while driving in 2016. He was taken to hospital and told he had suffered a stroke caused by undiagnosed type 2 diabetes. He described prolonged health and social consequences that followed.

Research links undiagnosed and poorly managed diabetes to an increased risk of long-term complications. A 2022 study in the BMJ found that failing to diagnose and manage diabetes raises the risk of dying from any cause by about 13 percent. A 2013 study cited by researchers reported a 73 percent increased risk of dementia among people diagnosed with diabetes. Diabetes UK reports that diabetes is linked to about 180 amputations in the UK every week.

Early diagnosis and management reduce the risk of serious outcomes. Experts encourage people who suspect they might have diabetes to ask their general practitioner for an HbA1c blood test, which measures average blood sugar levels over the previous two to three months. The test gauges how much sugar has attached to haemoglobin in red blood cells and is considered a reliable indicator of longer-term blood sugar control.

"If patients are concerned then they should ask their GP for this test," said Professor Andrew Hattersley, a diabetes expert at the University of Exeter. He noted that younger people are among the most likely to have undiagnosed diabetes because they visit doctors less often and because there is a lingering perception that type 2 diabetes is an "old person's" disease.

The Lancet study found people under 35 were least likely to be diagnosed, with just one in five aware they had the condition, a gap that public health experts say needs addressing. "Despite improvements over the past 20 years, underdiagnosis of type 2 diabetes remains a major challenge in the UK, particularly in young people," said Nikki Joule, policy manager at Diabetes UK. "With one in five adults now living with diabetes or prediabetes in the UK, this research shows there is still a long way to go in improving diagnosis and treatment."

The NHS offers free health checks through GP services for people aged 40 and over designed to pick up early warning signs of conditions such as high blood pressure, heart disease and type 2 diabetes. Clinicians say lifestyle measures—losing excess weight, eating a diet rich in vegetables and whole grains and regular physical activity—can substantially improve blood sugar control and, in some cases, put type 2 diabetes into remission. Research shows losing 5 to 10 percent of body weight can have a marked effect on blood glucose.

When lifestyle measures are insufficient, doctors typically prescribe metformin to help the body use insulin more effectively. Other medications can boost insulin production or slow sugar absorption, and some patients eventually require daily insulin injections. People diagnosed with diabetes are monitored with blood tests, eye checks and foot exams to detect complications early.

Some people with type 2 diabetes may have few or no obvious symptoms. Ken Heard, a 64-year-old college tutor who has a healthy body mass index, said dehydration and frequent urination were the only signs he noticed; he was diagnosed after seeing a poster offering diabetes checks and taking a test at a pharmacy. Marathon runner Tony Pidgeon, 57, described being surprised by a 2021 type 2 diagnosis despite many years of high activity and a healthy weight; he later took part in a low-calorie, low-carbohydrate trial aiming for remission.

Clinicians emphasise that visible skin changes, fluctuating vision and recurrent infections should not be ignored even when they are painless. "The trouble for many patients with type 2 diabetes is that the symptoms come on slowly and become part of everyday life," Professor Hattersley said. "Early treatment is crucial for preventing complications and long-term consequences."

For anyone noticing the described signs, doctors recommend contacting a GP and requesting an HbA1c test rather than waiting for symptoms to worsen.