What Causes Dark Toenails From Injury To Infection?

Dark toenails happen when blood collects under the nail or when the nail itself changes color from the inside out. The most common cause is a simple injury that breaks tiny blood vessels beneath the nail, creating a dark spot that can look alarming but is usually harmless. Infections, certain medications, and a few medical conditions can also darken a nail, and telling these apart matters because the treatment is completely different.

What Causes Dark Toenails From Injury to Infection?

Two very different problems can turn a toenail dark, and they often look similar at first glance.

Injury is the more common cause. When you drop something on your toe, stub it hard, or wear shoes that press on the nail for hours, small blood vessels under the nail can break. Blood pools in the space between the nail and the nail bed. This is called a subungual hematoma. The trapped blood looks red at first, then darkens to purple, brown, or black over the next day or two as it dries.

Infection works differently. A fungal infection grows in the nail itself, usually starting at the tip or side and spreading toward the base. It tends to cause yellow, brown, or grayish discoloration rather than the deep black of pooled blood. The nail may thicken, crumble, or lift away from the nail bed.

One distinction is worth remembering. A single dark spot that appeared right after a specific injury is almost always blood. Darkening that develops slowly across several nails, with no injury, points toward infection or another underlying cause.

What Does a Blood Blister Under the Toenail Look Like?

A subungual hematoma usually appears as a dark, well-defined patch under the nail. The color can range from deep red to near-black depending on how much time has passed.

Several features help identify it:

• It appears within minutes to hours of a known injury
• The color is uniform across the spot rather than patchy
• The spot stays in one place and does not spread to other nails
• The nail itself stays smooth unless the injury also cracked it
• There is often throbbing pain at first, which fades as pressure settles

The size of the dark area reflects how much blood collected. A small speck may cause no pain at all. A spot covering most of the nail can create enough pressure to cause significant throbbing, because the nail cannot expand to relieve it.

Over weeks, the trapped blood dries and the dark spot moves outward as the nail grows. Toenails grow slowly, so a spot near the base can take many months to grow out completely. This is normal and not a sign that something is wrong.

How Can You Tell If a Dark Toenail Is Fungal?

Fungal nail infections, called onychomycosis, tend to follow a different pattern than injury.

They usually start at the edge of the nail and move inward. The affected area often looks yellow or brown rather than black. The nail may become thick, brittle, or crumbly at the edges. In some cases the nail separates from the nail bed, a condition called onycholysis.

Fungal infections often affect more than one nail, especially on the same foot. They develop gradually over months, not overnight. Athlete’s foot or a history of sweaty footwear raises the likelihood.

Diagnosis is not always obvious by appearance alone. Different fungi and even some non-fungal conditions can produce similar changes. A clinician can confirm a fungal infection by examining a nail sample under a microscope or sending it for culture. This matters because antifungal treatment is lengthy and not without cost or side effects, so confirming the diagnosis first is reasonable.

When Is a Dark Toenail a Sign of Something More Serious?

Melanoma can develop under a toenail, though it is uncommon. It is the reason a new dark streak or spot that cannot be explained by injury deserves medical attention.

Signs that warrant a professional evaluation include:

• A dark streak or band running from the base of the nail to the tip, especially if it widens over time
• Darkening that extends onto the skin around the nail
• A dark spot with no history of injury
• Changes in a single nail that keep progressing
• Bleeding from under the nail without a clear cause

Subungual melanoma is rare. Most dark toenails are not cancer. But because it can look like a bruise that never heals, the distinction matters. A dark spot that stays the same for months while the nail grows out is likely old blood. A spot that grows, spreads, or changes shape needs a closer look.

Other conditions can also darken nails. Psoriasis can cause pits, ridges, and a brownish discoloration sometimes called an oil drop spot. Certain medications, including some chemotherapy drugs and antibiotics, can darken nails. These causes are less common than injury or fungus but are worth knowing about.

Should You Drain Blood From Under a Toenail?

Draining is a procedure called trephination. A clinician makes a small hole in the nail to release trapped blood and relieve pressure.

This is generally considered when pain is significant and the injury is recent. The timing matters. Once blood has clotted, draining becomes difficult or impossible, so the window for this procedure is limited. It should be done by a clinician using sterile technique, not attempted at home. Puncturing a nail yourself risks infection and injury to the nail bed.

For mild cases with little pain, no draining is needed. The blood simply grows out with the nail over time.

If the injury also broke the nail, damaged the nail bed, or there is an open wound, a clinician should assess it. Crush injuries that cause large hematomas can sometimes involve an underlying fracture, and that changes the approach.

How Are Fungal Toenail Infections Treated?

Fungal nail infections are hard to clear. The nail grows slowly, and topical treatments often struggle to penetrate the hard nail plate.

Treatment options include:

• Oral antifungal medications, which are generally more effective than topical products for moderate to severe infections
• Topical antifungal lacquers or solutions, which may help in mild cases
• Nail removal in severe or stubborn cases

Oral antifungals can affect the liver, so clinicians often check liver function before and during treatment. This is why confirming the diagnosis first matters. Treating a bruise with antifungal medication does nothing, and treating a fungus as a bruise lets it spread.

Even with successful treatment, the nail can take a year or longer to look normal because the damaged portion has to grow out. Reinfection is common, especially if the feet stay damp or the same shoes are worn without letting them dry.

What Helps a Dark Toenail Heal?

For an injury-related dark nail, time does most of the work. The blood reabsorbs or grows out with the nail.

A few practical steps can help in the meantime:

• Choose shoes with a wide toe box to reduce pressure on the nail
• Keep the toe clean and dry
• Avoid repeated trauma to the same toe
• Trim the nail straight across to avoid ingrown edges

If pain is significant, swelling is present, or the toe looks infected, see a clinician. Signs of infection include spreading redness, warmth, pus, or fever.

For fungal infections, keep feet dry, change socks when they get damp, and avoid sharing nail clippers or shoes with someone who has an infection. These steps lower the chance of spreading or reinfection but do not cure an established infection on their own.

How Long Does a Dark Toenail Take to Grow Out?

Toenails grow slowly, at roughly 1 to 2 millimeters per month. A big toenail can take 12 to 18 months to fully replace itself.

That means a dark spot near the base of the nail may take well over a year to disappear completely. A spot near the tip clears much faster. This timeline is worth knowing because it explains why a bruise can seem to linger forever even when nothing is wrong.

If the dark area is not moving outward with nail growth, or if it is growing larger, that is a reason to have it checked. Normal bruising moves with the nail. A spot that stays put or expands is behaving differently.