Chronic high blood sugar can cause changes to the nails.

Key Takeaways

Yellow or dull-looking nails can be an early sign of high blood sugar, due to the breakdown of sugar and its impact on collagen.
A new brown or black streak on the nail that changes or involves surrounding skin should be evaluated by a dermatologist to rule out melanoma.
High blood sugar can slow nail growth, make nails brittle, or increase the risk of fungal infections, which may cause thick, crumbly, or discolored nails.

Persistent elevated blood sugar can lead to a number of changes in the body, including your fingernails.

That’s because when a person’s blood sugar stays elevated for extended periods of time, it can affect the nerves and tiny blood vessels that supply the toes and nail beds. Nails are also a mirror of general health, so major changes in their appearance can indicate a deeper issue, such as diabetes. 1

1. Discoloration

One of the most common early signs of high blood sugar is a yellow or dull-looking nail, said Omodamola Aje, MD, a board-certified endocrinologist at Berkshire Medical Center. This kind of coloring can occur in the nails of people with diabetes because of the breakdown of sugar and its impact on collagen. While this type of mild discoloration can be a sign that something deeper is going on, it is typically harmless and does not need treatment.

However, Melanie Palm, MD, a board-certified dermatologist and clinical professor at the University of California, San Diego, said a new brown or black streak—particularly one that is changing, widening, or involving the surrounding skin—should be evaluated by a dermatologist rather than assumed to have anything to do with diabetes.

“Nail melanoma is uncommon, but it is something we do not want to miss,” she said.

2. Slow Growth

High blood sugar can also slow nail growth.

“Over time, poorly controlled diabetes can affect the small blood vessels and circulation that supply tissues throughout the body,” Palm explained. “That can affect how well the nail unit is nourished and how normally a nail grows.”

Chronic hyperglycemia can also damage nerves and blood vessels more broadly, she said.

3. Brittle Nails

In addition to discoloration and slow growth, high blood sugar can also cause nails to become brittle. They may crack and split easily, while clubbing can be seen in more advanced or long-standing cases, Aje said.

The nail may also become thicker than normal and even begin separating from the nail bed, Palm said. “That said, I would be careful about attributing every brittle or yellow nail directly to glucose issues.”

4. Infection

High blood sugar can impair immune function, increasing the risk of fungal infections of the nails, known as “onychomycosis.” 2

This may cause the nail to look yellow or white, become thicker, appear crumbly or distorted, and sometimes lift away from the nail bed, Palm said. In fact, all of the changes mentioned above can occur on their own or be caused by a fungal infection. While diabetes increases the risk of fungal nail infections, she said this tends to be even more noticeable in the toenails than the fingernails.

“Persistently elevated blood sugar can make it more difficult for the immune system to respond effectively to infection, and fungal infections are more common when blood glucose is high,” Palm explained. “That can become something of a cycle.”

If not properly treated, this kind of infection can lead to an elevated risk of secondary fungal and bacterial infections, foot ulceration, and, in advanced cases, amputation.2

When To Get Checked

While nail changes by themselves are not a way to diagnose high blood sugar or diabetes, Aje said they can be a useful early sign of the condition, especially in someone with risk factors such as obesity, a family history of diabetes, or a sedentary lifestyle.

“If you notice any changes in your nail color, brittleness, or thickness associated with an increased thirst, frequent urination, fatigue, or unexplained weight loss, definitely bring it up to your doctor,” she said.

However, it’s important to recognize there isn’t one specific “diabetes nail,” Palm said, and nail changes can only give clues about what may be happening elsewhere in the body. Nail changes may also have other potential causes, including aging, repeated wetting and drying of the hands, manicures, trauma, psoriasis, eczema, medications, and other medical conditions.

“Any nail change that is new, persistent, or getting progressively worse deserves attention, particularly if someone already has diabetes,” she said. “I’d want a patient evaluated if a nail becomes painful, swollen, warm, or increasingly red around the edges, or if there is drainage or another sign of infection.”

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4 Signs of High Blood Sugar in Your Fingernails, According to Doctors