A purple toenail, medically known as chromonychia, is a noticeable change in nail coloration. The dark blue or purple hue beneath the nail plate is typically a reaction to one of two physical processes: the presence of blood or a lack of oxygen. While this discoloration often results from a common, minor injury, it can also signal an underlying issue that requires attention. Understanding these causes helps determine if home care is sufficient or if professional medical evaluation is necessary.
The Most Common Cause: Subungual Hematoma
The most frequent reason for a toenail to turn purple is a subungual hematoma, a bruise beneath the nail plate. This discoloration occurs when trauma causes small blood vessels in the nail bed to rupture, leading to an accumulation of blood trapped between the nail and the underlying tissue. The color transition reflects the blood clotting and drying under the nail.
This injury results from a single, acute event, such as stubbing a toe or dropping a heavy object onto the foot. Repetitive, minor trauma is a more common cause, such as wearing tight shoes during running or hiking. Athletes often experience this discoloration, sometimes called “runner’s toenail,” when toes repeatedly hit the front of the shoe.
A subungual hematoma often causes throbbing pain and intense pressure because the blood has nowhere to expand. Small, painless hematomas are harmless and resolve as the nail grows out, a process taking 12 to 18 months. If pressure is severe, a medical professional may perform trephination, creating a small, sterile hole to drain the trapped blood and relieve pain immediately. Do not attempt draining the hematoma at home due to the high risk of infection and further damage.
Less Common Medical Causes of Discoloration
Not all purple discoloration stems from acute injury; some hues relate to long-term physical conditions. A bluish-purple tone that does not fade or grow out may indicate cyanosis, a symptom of poor oxygenation in the blood. This occurs when circulation issues prevent sufficient oxygen-rich blood from reaching the extremities. Conditions like peripheral artery disease (PAD) reduce blood flow due to plaque buildup, while Raynaud’s phenomenon causes small blood vessels to narrow in response to cold or stress.
A fungal infection (onychomycosis) is another distinct cause, sometimes resulting in dark discoloration, though it usually presents as yellow or white. Fungal infections cause the nail to thicken, crumble, or lift away from the nail bed. Systemic diseases, such as diabetes, can also increase the risk of toenail discoloration due to diminished circulation and higher infection rates.
In rare instances, a dark streak or patch can signal subungual melanoma, a serious form of skin cancer developing in the nail bed. Unlike a bruise that grows out with the nail, melanoma often appears as a dark band that may widen over time or spread to the surrounding skin. Any unexplained, persistent dark spot under the nail should be evaluated by a healthcare provider.
Diagnosis and When Professional Care is Necessary
Monitoring the purple toenail is the first step, but certain changes signal the need for professional medical attention. Prompt evaluation is required for any discoloration that appears without a known injury, spreads rapidly, or is accompanied by signs of infection.
Red flags include:
- Increasing pain
- Swelling
- Warmth around the nail
- The presence of pus
- A red streak extending from the toe
Individuals with conditions impairing circulation or wound healing, such as diabetes, should seek immediate care for any toenail injury or discoloration.
A healthcare provider typically begins with a physical examination and patient history to determine the cause. If a subungual hematoma is large or painful, the provider may drain the blood via trephination to alleviate discomfort. For suspected fungal infections, a small nail sample may be scraped for laboratory testing before prescribing targeted antifungal medication.
If the discoloration is not trauma-related, further investigation may involve tests for circulatory or systemic issues. In the rare case of suspected melanoma, a biopsy of the nail bed tissue is necessary for a definitive diagnosis. Professional diagnosis ensures that serious conditions are not overlooked and allows for appropriate treatment.