Changes to your skin and nails can be a red flag if you’re living with diabetes, especially when your feet are affected. If one or more of your toenails have turned black, it could point to many conditions, some of which require immediate care from a doctor.

Understanding the potential causes of the symptom can help you take appropriate steps to address and manage any underlying health concerns. In this article, we’ll explore five possible causes of black toenails in people with diabetes and what to do if you experience this symptom.

1. Diabetic Neuropathy

Uncontrolled diabetes causes damage to the nerves in the extremities, most often starting with the toes and feet. This complication is called diabetic neuropathy and often indirectly leads to foot and toe symptoms.

When you have nerve damage in your feet, you don’t receive pain signals from injury or overuse the same way as someone without diabetic neuropathy. You might wear shoes that don’t fit well or position your feet oddly and not feel any pain. This problem can lead to injuries that you might not notice. As a result, you’ll be at a higher risk for infected wounds and injuries that don’t bother you until they get significantly worse. This is a common reason why people with diabetes may experience blackened toenails and other toe and foot injuries.

If you or your primary care doctor notices that you have less feeling in your feet, make sure to examine your feet and toes every night. If you see a wound, make sure to take good care of it until it heals. See your doctor right away if you notice signs of infection or severe injury, such as blackened toes. Staying in control of your diabetes with diet, exercise, and medications is the best way to prevent diabetic neuropathy from worsening and prevent toe injury.

2. Peripheral Arterial Disease

Peripheral arterial disease (PAD), often seen in people with diabetes, causes reduced blood flow to the extremities. This condition occurs because the blood vessels that carry blood from the heart to the legs become narrower. When blood flow is limited, your toes don’t receive enough oxygen and nutrients. This process can directly lead to tissue damage that shows up in the form of color change, including blackened toenails and toes. If PAD isn’t treated, the mild initial stage can progress to more severe complications, so it’s important to get medical attention right away.

One severe complication of PAD is gangrene, a serious disease in which a lack of blood supply causes tissue to die. Gangrene usually starts at the extremities, including the toes. Symptoms include skin discoloration, which may be harder to see on darker skin. You may also see swelling or discharge coming from the affected area. Seek emergency medical care if you think you are experiencing gangrene, as it’s a potentially life-threatening condition.

3. Fungal Infection

Many types of fungal infections are common among people with diabetes, especially in those who have high blood glucose levels. Fungi thrive in warm and moist environments, making the feet an easy target, especially for people who sweat a lot or live in a humid climate. Toenail fungus can cause discoloration of the nails, including turning them black. Fungal nail infections, known as onychomycosis, begin with a white or yellow color change and result in nail thickening.

Treating fungal infections right away is essential to preventing further complications. Depending on the severity of the infection, your doctor may recommend treatments such as over-the-counter antifungal cream, ointments, or oral prescription medication. If your toenail infection is especially severe, your provider might recommend surgery to remove the nail and get better access to treat the fungal infection.

Treating fungal infections can take a while, but these infections should resolve with proper medical care.

4. Trauma or Injury

Accidental toe injuries are a common cause of blackened toenails in people with and without diabetes. Stubbing your toe, dropping a heavy object on your foot, having an ingrown toenail, or wearing tight shoes that constantly press on the nail can cause blood to accumulate beneath the nail, making it appear black.

Bleeding injuries beneath the toenail are called sbungual hematomas. This type of injury might first appear as a black spot. Combined with diabetic neuropathy (decreased sensation in your feet), trauma or injury can be more serious than you realize. Usually, a one-time injury such as stubbing your toe will get better on its own, but repeated trauma could affect the entire nail.

If you have a blackened toenail or another toe abnormality — whether or not it’s causing pain — see a podiatrist or your primary care doctor. To prevent injury or trauma to your toes, trim your toenails frequently and wear shoes that fit well. You’ll also want to pay attention to your surroundings to avoid tripping over obstacles, which is particularly important in unfamiliar or uneven terrain.

5. Medications

Sometimes, nail changes can be caused by drugs. Medications that cause black or brown bands on the nails include zidovudine (an HIV medication), psoralens (a psoriasis drug), and hydroxyurea (a chemotherapy drug). Bluish-gray coloration can be caused by minocycline (an antibiotic). Brown discoloration on the nail bed can be caused by antimalarial medications. Outside of rare cases, black coloration of the nails has not been reported as a common side effect of diabetes medications.

If you recently started a new medication and notice a new symptom or side effect such as black toenails, consult your health care provider for medical advice. Remember, proactive care is key to maintaining your foot health and overall well-being with diabetes.

Talk With Others Who Understand

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Have you ever had black toenails with diabetes? What did you do? Share your experience in the comments below, or start a conversation by posting on your Activities page.