Black or Discolored Toenail? Causes, Treatment, and When to Worry

A toenail that turns black, brown, or dark purple looks alarming, but most of the time the cause is simple: blood trapped under the nail after an injury or repeated pressure. Sometimes, though, a dark toenail points to a fungal infection or, rarely, something more serious. Here is how to tell what is behind a black toenail, what you can safely do at home, and when it needs a podiatrist's attention.

What causes a black toenail?

The most common cause is a subungual hematoma, which is blood pooling under the nail after you stub your toe, drop something on it, or wear shoes that are too tight. Runners and athletes often develop black toenails from the toe repeatedly hitting the front of the shoe, sometimes without any pain at all. Other causes include fungal infection, chronic ingrown nails, certain medications, and underlying conditions such as diabetes or anemia.

A black toenail without injury

A toenail turning black without an injury you can remember deserves a closer look. Painless dark discoloration can come from a slow-growing fungal infection, repeated micro-trauma you never noticed, or, rarely, subungual melanoma, a form of skin cancer that develops under the nail. The warning sign to know is a dark streak running from the base of the nail to the tip, especially one that widens over time or spreads onto the surrounding skin. If you see that pattern, have it evaluated promptly.

Is it a bruise or toenail fungus?

A bruise under the nail stays in one spot and slowly grows out with the nail over several months. Fungus behaves differently: it spreads, thickens the nail, and produces crumbly debris underneath, often turning the nail yellow-brown before it darkens. If your dark nail is also thick, brittle, or misshapen, a fungal infection is likely, and it will not clear up on its own. We treat fungal nails in our office, including with laser therapy.

Do black toenails fall off?

Often, yes. When enough blood collects under the nail, it separates the nail plate from the nail bed, and the loose nail eventually detaches as a new one grows in behind it. A big toenail takes roughly 6 to 12 months to fully regrow. Never rip a loose nail off yourself; trim what snags and let a podiatrist remove the rest safely if it is catching or painful.

How a podiatrist treats a black toenail

Seen within the first day or two after an injury, a painful hematoma can be drained in minutes through a tiny opening in the nail, which relieves the pressure immediately. Beyond that window, treatment focuses on the cause: testing the nail for fungus, protecting a loosening nail while the new one grows, fixing the footwear or activity pattern that caused it, and biopsying any suspicious pigmentation. Diabetic patients should have any dark toenail checked quickly, since reduced circulation and sensation raise the risk of complications.

Frequently asked questions

Why is only one toenail black?

Trauma and pressure usually affect a single nail, most often the big toe, so one black toenail typically means an injury or a shoe rubbing that specific toe. A single dark nail with no explanation is also the classic presentation of the rarer causes, so if it appeared on its own and is not growing out, get it examined.

How serious is a black toenail?

Most are harmless and resolve as the nail grows out. See a podiatrist if there was no injury, the discoloration is spreading, the nail is painful or draining, you have diabetes, or a dark streak extends from the cuticle to the tip.

How do I fix my toenail if it's black?

You cannot polish or bleach the color away, because it sits under the nail. Fresh, painful injuries can be drained for fast relief. Fungal nails need antifungal or laser treatment. Everything else is about protecting the toe while healthy nail replaces the damaged one.

Will a black toenail go back to normal?

If the cause was a bruise, yes. The dark area grows out with the nail and the new nail comes in normal, though it can take up to a year on a big toe. Nails damaged by severe injury or long-standing fungus can regrow thickened or irregular, which is why treating the cause early matters.

If a black or discolored toenail has you worried, do not wait it out. Dr. Jonathan Mollineda, DPM at Sunshine Foot and Ankle LLC treats nail injuries, fungal nails, and everything in between for patients of all ages, from kids to seniors. Call (754) 296-5900 or book online at sunshinefootandankle.com/book-online. Our office is located at 2951 NW 49th Ave, Suite 204, Lauderdale Lakes, FL 33313, serving Lauderdale Lakes, Lauderhill, Tamarac, Plantation, and the greater Fort Lauderdale area.