A purple or dark discoloration beneath a toenail, medically known as chromonychia, is a common symptom that often prompts concern. This change in color signals an underlying issue affecting the nail bed or the nail plate itself. While the appearance can be alarming, the causes range from benign injuries to more serious health conditions requiring medical attention.
The Primary Cause: Subungual Hematoma
The most frequent reason a toenail turns purple is a subungual hematoma, which is simply a bruise beneath the nail plate. This occurs when physical trauma causes small blood vessels in the underlying nail bed to rupture and leak blood into the confined space. Because the blood has nowhere to escape, the pressure causes the immediate purple or reddish-black appearance and often intense throbbing pain.
Acute causes include dropping a heavy object on the toe or forcefully stubbing it. Damage is often the result of repetitive, minor trauma, such as a runner’s toe, where the nail repeatedly impacts the front of an ill-fitting shoe. The purple hue represents fresh blood, which gradually changes to a darker brown or black as it dries and coagulates.
A subungual hematoma resolves naturally as the affected nail grows out, pushing the discoloration forward from the nail matrix. This process is slow, taking six to twelve months for the toenail to be completely replaced. If the injury was severe, the nail may loosen and eventually fall off, allowing a new, healthy nail to grow.
Non-Injury Related Reasons for Discoloration
Not all purple discoloration is due to physical impact; sometimes, it indicates a systemic or biological issue. A common non-injury culprit is a fungal infection (onychomycosis), which can cause the nail to thicken and turn yellow, brown, or a dark purplish color. The fungal organisms thrive in the warm, moist environment of the foot, often leading to crumbling or lifting of the nail plate.
Discoloration can also signal circulation issues, causing the toe to appear blue or purplish due to a lack of oxygenated blood. Conditions like Raynaud’s phenomenon involve the narrowing of small arteries in response to cold or stress, restricting blood flow and temporarily turning the digits blue or purple. Peripheral artery disease (PAD) is a serious circulatory concern where plaque buildup narrows the blood vessels, leading to chronic discoloration and potential tissue damage.
A rare but serious cause of unexplained dark streaks or patches is subungual melanoma, a form of skin cancer that develops in the nail bed. Unlike a hematoma, which appears after an injury and grows out with the nail, melanoma often presents as a dark, vertical band that is not associated with trauma. This pigmentation is caused by an overproduction of melanin and should be evaluated immediately, particularly if the discoloration extends to the skin around the nail.
Recognizing Warning Signs and Next Steps
Most minor, trauma-induced purple toenails can be managed with home care, including rest, elevation, and applying ice to reduce swelling. However, certain symptoms warrant an immediate visit to a healthcare provider. Severe, unmanageable pain or intense throbbing that does not subside after a day suggests significant pressure from the blood buildup.
Signs of infection, such as increasing redness, warmth, swelling, or pus draining from beneath the nail fold, require immediate attention. If the discoloration covers a large portion of the nail and is accompanied by a deep cut or laceration, medical attention is necessary to assess for fracture or damage to the nail matrix.
For a large, painful hematoma, a doctor may perform trephination, which involves using a sterile needle or cautery device to create a small hole in the nail plate. This instantly releases the trapped blood and relieves the pressure.
If the purple color appeared without any known injury, or if a dark streak does not migrate forward as the nail grows, a professional evaluation is necessary. This evaluation helps rule out fungal infection, circulatory disease, or the rare possibility of melanoma.