Dark skin on your knuckles can have many causes. The darker pigmentation on your knuckles may be inherited. Or it may be a reaction to a drug you’re taking, such as an oral contraceptive, a strong corticosteroid, products containing steroids or niacin.
Darker skin on your knuckles can also be a sign of an underlying condition that needs to be treated, such as diabetes.
Anyone at any age can develop dark knuckles.
Acanthosis nigricans (AN) is a condition that involves darkening and thickening of the skin in one or more areas on the body, including the knuckles. The darkened skin may feel velvety. It may also feel itchy or have an odor.
Prediabetes and diabetes
Dark knuckles are most prevalent among people who have diabetes or who have several risk factors for diabetes. Prediabetes means that your blood sugar levels are higher than normal.
According to the Mayo Clinic, prediabetes often has no symptoms, so darkened knuckles can be a warning sign. This is important, because lifestyle changes can help regulate your blood sugar levels and prevent prediabetes from progressing to diabetes.
The relationship of dark knuckles and diabetes isn’t fully understood. It’s thought that high levels of insulin may affect the growth of skin cells.
Vitamin B-12 deficiency
According to a 2016 study, dark knuckles can be an important marker for vitamin B-12 deficiency. Sometimes it may be the only marker for this deficiency. Other symptoms of vitamin B-12 deficiency include:
- shortness of breath
- feeling dizzy or light-headed
- neurological problems
A 2017 case study reported that about 10 percent of people with vitamin B-12 deficiency have darkened knuckles.
When B-12 deficiency is treated, the skin on the knuckles will likely return to their normal color.
Some people may develop darkened knuckles because of a drug they’re taking. The most common drugs that can cause this include:
- oral contraceptive pills
- growth hormone therapy
- estrogen therapy
- protease inhibitors
- niacin and nicotinic acid
- injected insulin
If you’re taking one of these drugs, you may want to discuss alternatives with your doctor. The knuckle darkening usually disappears once you stop taking the drug.
Dermatomyositis is a rare inflammatory disease that can cause muscle weakness and a skin rash. The rash can appear on the knuckles as well as on the face, chest, knees, or elbows.
The rash can be bluish-purple or red in color. Sometimes the rash can appear without any muscle symptoms.
Dermatomyositis most commonly occurs in children between 5 and 15 years old, or adults in their late 40s to early 60s. There’s no cure for this condition, but symptoms can be treated.
Addison’s disease is a rare condition. It’s caused by the failure of your adrenal glands to produce enough of the steroid hormones known as cortisol and aldosterone.
Fatigue and darkening in skin color are two common symptoms. The darker skin tends to appear near scars or skin creases like the knuckles. Symptoms can vary, but skin darkening often precedes other symptoms.
About 1 in 100,000 people in the United States has Addison’s disease. It usually affects people between 30 and 50 years old. The condition is treatable with drugs to manage symptoms.
Scleroderma, also called systemic sclerosis, is a rare autoimmune disease that causes an overproduction of collagen. This leads to the hardening and tightening of the skin and connective tissues. There are many types of scleroderma, and some can be disabling.
One of the symptoms of scleroderma is a reddening of the skin, including your hands and knuckles.
This condition is also linked to Raynaud’s phenomenon, which is often an early symptom of scleroderma. In Raynaud’s, the blood vessels in your fingers and toes contract and may turn blue and painful. This is usually in response to cold temperatures or stress.
Polycystic ovary syndrome
Polycystic ovary syndrome (PCOS) involves the production of higher-than-normal levels of male hormones in women. One of the symptoms may be darkening of the skin, especially in body creases.
PCOS is treatable with drugs and lifestyle changes, such as weight loss and exercise.
In rare cases, dark knuckles may be associated with an autoimmune disease such as Sjögren’s syndrome or lupuHi