A purple toenail almost always means blood has pooled beneath the nail plate, a condition called a subungual hematoma. A single hard knock, weeks of friction from tight shoes, circulation problems, certain medications, and on rare occasions a serious growth under the nail can all produce that alarming discoloration. Most cases are harmless and resolve on their own, but the overlap between a simple bruise and something that deserves medical attention is worth understanding in detail.
Subungual Hematoma From Acute Injury
The most straightforward reason a toenail turns purple is blunt trauma. Dropping something heavy on your foot, stubbing your toe on a door frame, or having your foot stepped on can rupture tiny blood vessels in the nail bed. Because the nail plate sits tight against the tissue underneath, the blood has nowhere to drain. It collects into a visible pool that shows through the nail as a dark red, purple, or almost black patch.1Haemophilia. Hand and Foot Subungual Haematomas in Haemophilia: A Report of Six Cases The discoloration typically starts within hours of the injury and can be intensely painful because pressure builds in the confined space under the nail.
Under magnification, these hemorrhages appear as well-defined dots or blotches ranging from red to red-black in color.2British Journal of Dermatology. Dermoscopy of subungual haemorrhage: its usefulness in differential diagnosis from nail‐unit melanoma You can often remember the specific incident that caused the bruise, which is the most helpful clue that it is benign. If the hematoma covers less than about a quarter of the nail and the pain is tolerable, it will usually grow out with the nail over the course of several months. The big toenail, being the largest and most exposed, is the one most commonly affected.
Repetitive Microtrauma and Tight Footwear
Not every purple toenail traces back to one dramatic event. Distance runners, hikers, and people who spend long hours on their feet in poorly fitting shoes often develop what some call “runner’s toe” or “black toenail.” Each step nudges the toe forward into the front of the shoe, and over hundreds or thousands of repetitions, the cumulative impact damages the same nail bed capillaries that a single hard blow would rupture. The result looks identical to a trauma-induced hematoma, just without a single memorable cause.
Shoes that are too narrow, too short, or laced too loosely tend to be the biggest culprits. When your foot slides forward with each stride, the longest toenail (usually the big toe, but sometimes the second toe if it extends further) absorbs repeated contact with the shoe’s toe box. Downhill walking and running make the problem worse because gravity shifts your foot forward. People often discover the discoloration days after a long hike or race, sometimes assuming it appeared “out of nowhere.” The treatment is the same as for any subungual hematoma: let the nail grow out and address the footwear problem to prevent a recurrence.
Poor Circulation and Cyanosis
When purple discoloration affects the skin around and beneath the nail rather than forming a discrete blotch, circulation is the more likely explanation. In this scenario, the color change is not from trapped blood but from blood that is not carrying enough oxygen. Deoxygenated blood is darker, giving the nail bed and surrounding tissue a blue-purple hue.
Raynaud’s phenomenon is one of the more common vascular causes. In response to cold or stress, the small arteries supplying the toes clamp down dramatically, temporarily starving the tissue of oxygen. The toes may turn white, then blue or purple, and finally red as blood flow returns. Episodes are usually brief but can be alarming. Peripheral artery disease, which involves a chronic narrowing of the arteries in the legs and feet, produces a more constant version of the same color change. People with diabetes, uncontrolled high blood pressure, or a history of smoking are at higher risk.
Heart and lung conditions that reduce the overall oxygen saturation of the blood can also cause a purple or bluish tint across multiple nails at once. If the discoloration is present in several toenails and fingernails simultaneously, that pattern points away from a localized bruise and toward a systemic issue worth discussing with a doctor promptly.
Splinter Hemorrhages and What They Signal
Sometimes the purple discoloration is not a broad blotch but a thin, dark line running lengthwise under the nail. These are called splinter hemorrhages because they look like tiny splinters embedded in the nail bed. They form when blood leaks out of the small longitudinal vessels beneath the nail, then attaches to the underside of the nail plate and migrates toward the tip as the nail grows.3PubMed Central. Nitrofurantoin-induced splinter hemorrhages: A forgotten culprit
Trauma is again the leading cause, but splinter hemorrhages carry a longer list of possible triggers than the broad hematomas described earlier. They can be associated with:
- Bacterial endocarditis: An infection of the heart valves that showers tiny clots into the bloodstream, some of which lodge in the nail bed vessels.
- Diabetes: Chronic blood sugar elevations damage small vessels, making them more prone to leaking.
- Skin conditions: Psoriasis, fungal nail infections, and certain autoimmune conditions can inflame the nail bed enough to cause small hemorrhages.
- Medications: Antibiotics, sedatives, and targeted cancer therapies have all been implicated.
A single splinter hemorrhage on one toenail, especially if you can recall bumping it, is rarely a concern. Multiple splinter hemorrhages across several nails, particularly if you also have a fever, fatigue, or unexplained weight loss, warrant a medical evaluation. Endocarditis in particular is a condition where early detection changes outcomes significantly.3PubMed Central. Nitrofurantoin-induced splinter hemorrhages: A forgotten culprit
Medications That Change Nail Color
A purple or dark discoloration of the toenail can show up as a side effect of a surprisingly wide range of drugs. Chemotherapy agents are among the best known offenders, but they are far from the only ones. Research on drug-induced nail pigmentation has identified involvement from alkylating agents, antimalarials, antimicrobials, antiretrovirals, anticoagulants, antiepileptics, certain pain medications, and even some psychiatric drugs.4PubMed. An Update on Drug-Induced Pigmentation
The color can range from faint brownish-purple bands running along the length of the nail to a diffuse darkening of the entire nail plate. The mechanism varies by drug class. Some stimulate the melanocytes (pigment-producing cells) in the nail matrix to deposit extra pigment, while others damage the nail bed capillaries directly, producing hemorrhage-type discoloration. The antibiotic nitrofurantoin, commonly prescribed for urinary tract infections, is one example that can cause splinter hemorrhages resembling those from vascular causes.3PubMed Central. Nitrofurantoin-induced splinter hemorrhages: A forgotten culprit
If you notice a toenail changing color within weeks of starting a new medication, mention it to your prescribing doctor. The discoloration itself is usually cosmetic and reversible once the drug is stopped, but confirming the cause avoids unnecessary worry about more serious explanations.
Telling a Bruise From Melanoma
This is the question that drives most of the anxiety around purple toenails, and for good reason. Subungual melanoma, a form of skin cancer that develops in the nail bed, can look strikingly similar to a simple bruise in its early stages. The differential diagnosis ranges from harmless, self-limiting conditions like subungual hematoma to potentially fatal ones like melanoma.5PubMed. Pigmented Nail Lesions: When to Observe, When to Biopsy, When to Widely Excise, and When to Amputate? Some cases are difficult to distinguish from melanoma with the naked eye alone.2British Journal of Dermatology. Dermoscopy of subungual haemorrhage: its usefulness in differential diagnosis from nail‐unit melanoma
Fortunately, several features help separate the two. A subungual hematoma is a defined, static collection of blood that gradually moves toward the tip of the nail as it grows out. Over weeks and months you can watch the leading edge of the dark spot march forward. A melanoma, by contrast, tends to present as a longitudinal dark band running from the base of the nail to the tip. As it progresses, the band may widen and the coloring may become irregular, with mixtures of brown, black, and purple. One particularly worrying sign is the Hutchinson sign: dark pigment that spills beyond the nail plate onto the surrounding skin of the nail fold.6Dermatology. Examination of Subungual Hematomas and Subungual Melanocytic Lesions by Using Optical Coherence Tomography and Dermoscopy
There is a complicating wrinkle. After a severe bruise, blood can sometimes seep into the soft tissue of the nail fold and produce a “pseudo-Hutchinson sign” that mimics the real thing. In one documented case, that dark discoloration appeared on the proximal nail fold about two weeks after an injury but resolved entirely by sixteen weeks, with the dark area on the nail plate migrating distally as normal growth proceeded.7PubMed Central. Trauma-Associated Pseudo-Hutchinson Sign: An Autobiographical Case Report Emphasizing Conditions, Pseudo-Conditions, and Pseudo-Pseudo-Conditions This resolution pattern is the key difference: a bruise-related pseudo-Hutchinson sign fades and grows out, whereas a true Hutchinson sign from melanoma persists and worsens.
The practical takeaway: if you have a dark spot under a toenail and you remember the injury that caused it, you can generally monitor it at home. Take a photo every two to four weeks. If the dark area migrates toward the tip of the nail and shrinks over time, you are watching a hematoma resolve. If a new band of color appears from the base that does not move, if the pigment spills onto the surrounding skin and does not go away, or if you have no memory of an injury at all, get to a dermatologist. Subungual melanoma is rare, but it is disproportionately diagnosed late precisely because people assume the discoloration is just a bruise.
When and How Subungual Hematomas Are Treated
Most small subungual hematomas need no treatment at all. The blood resorbs or grows out with the nail over a few months. The toenail may eventually detach as a new nail grows in underneath, which looks worse than it sounds and is usually painless by that stage.
Large or acutely painful hematomas are a different matter. When blood pressure under the nail is intense enough to cause throbbing pain, a procedure called nail trephination can provide fast relief. A doctor creates a small hole through the nail plate, allowing the trapped blood to drain. Research on a controlled drilling technique found that the procedure successfully evacuated the hematoma with substantial pain relief over the following eight hours, minimal discomfort, and minimal risk to the underlying nail bed.8American Journal of Emergency Medicine. Controlled nail trephination for subungual hematoma Traditional methods use a heated paper clip or a needle to melt or punch through the nail, but the principle is the same: relieve the pressure and let the blood out.
If you decide to wait it out rather than seeking drainage, keep the nail clean and watch for signs of infection such as increasing redness, warmth, swelling, or pus. A hematoma that covers more than half the nail area, or one accompanied by a suspected fracture of the underlying bone, generally deserves a professional look. An X-ray can rule out fracture, and the doctor can decide whether the nail needs to be partially or fully removed to inspect the nail bed for damage.
Foot Deformities and Chronic Nail Pressure
People who deal with recurring purple toenails without obvious trauma sometimes have an underlying structural issue in the foot that puts chronic pressure on specific toes. Hammer toe, where one or more of the smaller toes bend upward at the middle joint, is a common example. The bent toe presses against the top or front of the shoe differently than a straight toe would, concentrating force on the nail with every step. Research using biomechanical modeling has shown that hammer toe deformity shifts where peak stress falls in the forefoot, with internal tissue stress roughly one and a half times greater than the plantar pressure alone would suggest.9PubMed. Associations between changes in loading pattern, deformity, and internal stresses at the foot with hammer toe during walking; a finite element approach That extra mechanical load on the soft tissue can damage the nail bed repeatedly, leading to chronic or recurrent hematomas.
Bunions, overlapping toes, and unusually long second toes can create similar patterns. If you keep bruising the same toenail despite switching to properly fitted shoes, a podiatrist can evaluate whether your foot’s anatomy is part of the equation. Solutions range from toe spacers and padding to orthotic inserts that redistribute pressure. Corrective surgery exists for severe deformities, though it is rarely performed solely for the sake of a bruised nail.
Fungal Infections and Other Mimics
Not every dark toenail is a bruise or a melanoma. Fungal nail infections, while most often associated with yellowing and thickening, occasionally produce dark brown or greenish-black discoloration that can read as purple under certain lighting. A secondary bacterial infection from Pseudomonas, which thrives in moist environments, is known for creating a distinctive green-black hue sometimes called “green nail syndrome.” These infections are more common in people whose nails are already damaged, making them an occasional companion to the repetitive trauma described above.
Nail psoriasis is another mimic. It can produce tiny hemorrhages in the nail bed that look like splinter hemorrhages from vascular causes, alongside pitting, ridging, and separation of the nail from the bed. If your toenails have changed color and you also have scaly patches on your skin or scalp, psoriasis is worth investigating as the shared cause.
Finally, melanonychia striata, a longitudinal brown or black band in the nail, can appear without any disease at all. It is common in people with darker skin tones and is caused by normal melanocyte activation in the nail matrix. A single stable band that does not widen or change over time is almost always benign, but any new band in someone who has not had one before deserves at least a baseline evaluation from a dermatologist, especially if the band is wide, irregularly colored, or affects only one nail. The anatomy of the nail unit, with its tightly layered structures and rich blood supply, means that a surprising number of conditions all converge on the same visible result: a dark toenail.10PubMed. Nail anatomy