A dark discoloration on a toenail, particularly the pinky, often triggers immediate worry. A black toenail is a common occurrence that is usually the result of a simple injury. The discoloration signifies a change beneath the hard nail plate, which can range from trapped blood to pigment changes. Understanding the cause and recognizing the signs that require professional attention is important for managing this common foot issue.
The Most Common Cause: Subungual Hematoma
The most frequent reason for a black toenail is a subungual hematoma, a bruise beneath the nail. This condition occurs when small blood vessels in the nail bed rupture, causing blood to pool between the nail and the toe bone. The initial appearance is often reddish-purple, quickly darkening to deep brown or black as the blood dries.
Repetitive microtrauma from activities like running, hiking, or walking in ill-fitting shoes can cause a hematoma, sometimes called “runner’s toe.” The pinky toe is particularly susceptible because it often receives pressure from narrow shoe toe boxes. The pressure from the pooled blood can cause a throbbing sensation and tenderness.
The discoloration will naturally grow out with the nail over time. Because toenails grow slowly, this process can take nine to twelve months for the pinky toenail to be fully replaced. If the hematoma covers a large portion of the nail and causes intense pain, a medical professional may drain the blood to relieve pressure, a procedure called trephination.
Other Potential Causes of Discoloration
Not all black toenails are related to trauma; other factors can cause discoloration beneath the nail plate. Fungal infections (onychomycosis) are common and can result in a dark appearance. While often yellowish or white, the infection can also appear black, brown, or grayish due to debris buildup or specific fungal species.
A fungal infection typically looks less uniform than a bruise and may be accompanied by a thickened or crumbly texture. Certain medications, including some chemotherapy drugs and antibiotics like minocycline, can also cause pigment changes. These drug-induced discolorations usually resolve after the medication is discontinued.
A more serious, though rare, cause is subungual melanoma, a form of skin cancer that develops under the nail. This condition often presents as a dark, persistent streak or band that appears suddenly without injury. Indicators of concern include irregular borders, multiple colors within the streak, or the pigment spreading to the cuticle or surrounding skin.
Deciding When to See a Doctor
Certain warning signs indicate the need for a medical evaluation regarding a black toenail.
- The discoloration appeared without any known trauma or injury.
- The pain is severe or throbbing and does not improve with rest and ice.
- There are signs of infection, such as increasing redness, swelling, warmth, or the presence of pus.
- The dark pigment extends beyond the nail plate onto the skin of the cuticle or nail fold (Hutchinson’s sign).
- The dark area does not shift or grow out with the rest of the nail over several months.
- The entire nail feels loose, or a fracture in the underlying bone is suspected due to a major injury.
Basic Care and Prevention Strategies
For a new black toenail caused by a minor injury, immediate care helps manage symptoms and prevent complications.
Immediate Care
Applying a cold compress or ice pack to the toe for the first 24 to 48 hours can reduce swelling and discomfort. Keeping the foot elevated and resting the digit also minimizes pressure and pain.
Prevention Strategies
Long-term prevention focuses on reducing the risk of trauma. Ensure that all footwear, especially athletic shoes, are properly sized with adequate room in the toe box. A proper fit allows a thumb’s width of space between the longest toe and the shoe tip.
Practice proper nail trimming techniques by cutting toenails straight across and keeping them relatively short. This prevents the nail from catching on socks or the shoe’s interior, reducing repetitive impact. Maintaining dry and clean feet also limits the environment where fungal infections can thrive.