Dirty patches on the skin? Be careful, as it may be a sign of diabetes.
Look at your body, especially in the folds of your skin, for brown or black patches that feel rough or even smell bad. This embarrassing condition often mistaken for ‘poor hygiene’ is actually acanthosis nigricans.
The patches of acanthosis nigricans have no clear borders and are symmetrically distributed. They often appear in skin folds or in areas prone to friction.
Common areas: back and side of neck, groin, and underarm, of which more than 90 percent of the time will appear on the neck.[1]
Uncommon areas: waist (where it rubs against the waistband), under the breast, front of the elbow, and back of the knuckles. In severe cases, lesions may even appear in areas such as the navel, lips, and mouth.
Why do people get acanthosis nigricans? It has nothing to do with personal hygiene habits, but it is a warning sign for the body. There are several common causes why people develop acanthosis nigricans:
Yilun Chiang, the attending physician of the Department of Endocrinology of Shin Kong Wu Ho-Su Memorial Hospital in Taiwan, pointed out that the precise mechanism that causes acanthosis nigricans is not fully understood. However, it is currently believed that the excessive secretion of insulin is one of the important factors.
Under normal conditions, insulin brings blood sugar into cells to stabilize blood sugar levels. When the body becomes less sensitive to insulin and forms insulin resistance, it must secrete more insulin to stabilize blood sugar. Excessive insulin can stimulate cell proliferation of skin cells, and cause melanin precipitation and hyperkeratosis (thickening of the skin’s outer layer), which eventually leads to acanthosis nigricans. 
Insulin resistance is an early sign of Type 2 diabetes. It can be improved with prompt treatment and adjustment of diet and lifestyle. If left unchecked, it can develop into Type 2 diabetes.
People with insulin resistance are often characterized by obesity or high waist circumference in addition to localized skin darkening and thickening. Individuals with such conditions also sometimes suffer from metabolic syndrome.
A survey of adolescents found that acanthosis nigricans was strongly associated with obesity, family history of diabetes, high blood pressure, and low physical activity; while obesity had the strongest association with acanthosis nigricans.[2]
People with Type 1 diabetes and Type 2 diabetes can also develop acanthosis nigricans. Liu Peng-Tzu, the attending physician of the Family Medicine Department of Shin Kong Wu Ho-Su Memorial Hospital, said that some children with Type 1 diabetes will develop acanthosis nigricans, even if they are not obese. He explained that although this group of people do not have insulin resistance, they can also experience skin discomfort or changes if they have high blood sugar.
Disorders such as polycystic ovary syndrome (PCOS), hypothyroidism, and adrenal insufficiency can also lead to cell proliferation.
Some medications can affect insulin secretion or cause insulin resistance-like conditions, such as birth control pills, corticosteroids, diethylstilbestrol (nonsteroidal estrogen), niacin and its derivatives, growth hormone, medication for thyroid treatment, etc.
Malignant acanthosis nigricans is mostly associated with adenocarcinomas of abdominal organs, especially gastric cancer. Patients with pancreatic, ovarian, breast, or esophageal cancers may also develop acanthosis nigricans. Acanthosis nigricans associated with cancer can occur before, with, or after the diagnosis of cancer.[3]
Other factors that cause acanthosis nigricans include genetic inheritance, autoimmune diseases, and so on.
Yilun Chiang said that the age of onset of acanthosis nigricans can range from infants to adults. Acanthosis nigricans is more likely to occur in adults than in children if it is caused by malignant tumors.
Are dark and dirty patches on the skin a sure sign of acanthosis nigricans?
Yilun Chiang pointed out that acanthosis nigricans have another characteristic: the affected area is usually not very itchy. Generally, the affected area of mild acanthosis nigricans will look dirty; as the symptoms worsen, the area will gradually expand and thicken, and the skin lines will deepen as well; there may even be wart-like growths on the epidermis.
Liu Peng-Tzu said that he would ask the patient if the affected area is itchy and whether they often feel the urge to scratch it.
If the patient says yes, then it is usually due to atopic dermatitis. Atopic dermatitis is characterized by itching of the affected area; local inflammation caused by excessive scratching can cause melanin deposition, making the affected area look dark and dirty.
As acanthosis nigricans is more common in people with insulin resistance and diabetes, doctors will prioritize screening for the disease when diagnosing people at high risk for diabetes.
As a result, some people were found to be prediabetic after undergoing blood tests which typically show a fasting blood glucose level between 100 and 125 mg/dL, or hemoglobin A1c level between 5.7 and 6.4 percent. The insulin resistance index (HOMA-IR) can also be measured. If the ratio of fasting blood glucose and blood insulin calculated by the formula is greater than or equal to two, it means that the patient has insulin resistance.
There are also people diagnosed with diabetes. In Liu Peng-Tzu’s outpatient clinic, it is common to see office workers in their 30s with acanthosis nigricans. These patients come to the clinic for examinations because of their skin abnormality that affects their appearance and cannot be removed after thorough cleaning.
One of the patients had a high BMI of about 29 (kg/m2), but did not show typical symptoms of diabetes (eating and drinking frequently, urinating more, and losing weight). However, his fasting blood glucose was between 130 and 150 mg/dL; medically it is considered diabetes if it exceeds 126 mg/dL.
The patient said that he was told that his blood sugar was too high during the medical examination at the university, but he did not pay special attention to it as he did not experience any symptoms. After more than 10 years, he not only developed acanthosis nigricans but also suffered from diabetes due to having insulin resistance for years.
Liu Peng-Tzu pointed out that most patients suffer from long-term insulin resistance or severe diabetes before they develop acanthosis nigricans.
There is currently no specific treatment for acanthosis nigricans. The main way to deal with acanthosis nigricans is to treat the cause and allow the affected area to improve naturally.
Insulin resistance and diabetes are the main causes of acanthosis nigricans; improving insulin resistance and controlling blood sugar can prevent the condition from getting worse.
“The most important thing is to address the fundamental problem of insulin resistance,” Liu Peng-Tzu said. For example, many patients with acanthosis nigricans are obese, so they should adjust their diet, exercise more, and actively lose weight.
The skin will slowly metabolize. The color of the affected area will gradually fade as the condition improves and the inflammation of the affected area is reduced.
In addition to treating the disease, there are several ways to prevent acanthosis nigricans from getting worse:
However, acanthosis nigricans will not go away completely and will still look somewhat different from the surrounding normal skin. Tsai Yi-shan, director of the dermatology department of the Yes Clinic in Taiwan, pointed out that the dermatology treatment method is to use vaporized lasers or provide some acid ointments to help the skin metabolize. While these methods can improve the affected skin slightly, there is no way to remove it completely.
It should be noted that acanthosis nigricans will recur if patients do not control their blood sugar and weight well in the future. People who have had acanthosis nigricans are more likely to have a recurrence of the disease than those without a history of the disease.


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