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Spotting a black toenail can be surprising—and even a little unsettling. A discolored toenail often raises concerns about injury, infection, or something more serious, whether it appeared after a long run, a stubbed toe, or with no apparent cause.

This article will explore what causes black toenails, how to tell when it’s harmless versus problematic, and when it’s time to see a specialist.

What Is a Black Toenail?

A black or darkened toenail typically means there’s been bleeding, bruising, or pigment changes beneath the nail plate. This condition is known medically as a subungual hematoma when caused by trauma, though there are several possible explanations depending on your symptoms and lifestyle.

Most Common Causes of a Black Toenail

1. Trauma or Repeated Impact

The most frequent cause of black toenails is injury—either a single impact (like dropping something heavy on your toe) or repetitive microtrauma from activities like running or hiking. The nail becomes discolored due to bleeding under the nail bed.

Signs to look for:

• Pain and tenderness
• Swelling around the nail
• Pressure under the nail
• The nail may eventually loosen or fall off

2. Fungal Infection

Some fungal infections can darken the nail over time, especially if left untreated. The discoloration may appear brown, yellow-black, or gray, often accompanied by nail thickening or crumbling.

3. Underlying Skin Conditions

Certain skin disorders, such as psoriasis or lichen planus, can affect the nail’s color and structure, occasionally leading to darkening or discoloration.

4. Melanoma (Rare but Serious)

In rare cases, a black line or dark spot under the toenail that doesn’t go away could be a sign of subungual melanoma, a form of skin cancer. This is not caused by trauma and may be accompanied by pigment extending to the surrounding skin.

Warning signs:

• No known injury
• The discoloration is spreading
• Involves the cuticle or surrounding skin
• Irregular borders or multiple colors

When to Be Concerned About a Black Toenail

While most black toenails are due to minor issues like bruising or pressure, you should seek medical advice if:

• The toenail turns black without any known injury
• There’s increasing pain or signs of infection (pus, warmth, redness)
• The nail is lifting or separating
• The color or size of the dark spot changes over time
• The discoloration extends beyond the nail itself

A foot and ankle specialist can help determine whether you’re dealing with trauma, fungus, or something that needs further testing.

How Are Black Toenails Treated?

Treatment depends on the underlying cause:

• Minor Trauma: May require no treatment beyond rest, ice, and protection
• Painful Hematoma: Draining the blood under the nail may relieve pressure
• Fungal Infection: Antifungal creams, oral medications, or laser therapy
• Melanoma: Referral to a dermatologist or oncologist for further evaluation

In some cases, the nail may fall off and gradually regrow over the course of 6–12 months.

Tips to Prevent Black Toenails

• Wear properly fitting shoes with enough toe space
• Trim your toenails straight across to prevent lifting or pressure
• Choose moisture-wicking socks and keep your feet dry
• Use protective footwear during high-risk activities
• Treat fungal infections promptly

Final Thoughts

A black toenail isn’t always a cause for alarm—but it’s not something to ignore either. Most cases are the result of trauma or fungus and resolve with conservative care. Still, monitoring changes and seeking help if the discoloration is unexplained or persistent is essential.

If you’re unsure about a black toenail or concerned about what it could mean, our expert podiatry team is here to help.