A toe turning black can result from something as harmless as stubbing it against furniture or as serious as tissue death from blocked blood flow. The color change itself is not a diagnosis; it is a signal that something has happened beneath the skin or nail, and the range of possibilities spans from minor trauma to melanoma to vascular emergencies. What matters most is how quickly the discoloration appeared, whether it is spreading, and whether you have pain, numbness, or other symptoms alongside it.
Trauma and Subungual Hematoma
The single most common reason for a black toe is bruising under the toenail after an injury. You drop something heavy on your foot, kick a hard surface, or wear shoes that are too tight during a long run, and blood pools beneath the nail plate. This is called a subungual hematoma, and it refers to the accumulation of blood under the nail due to traumatic injury.1PubMed Central. Subungual Hematoma: Insights From a Clinical Case Study The trapped blood turns the nail dark purple, blue, or black. Sometimes you remember the exact moment it happened; other times, repeated micro-trauma from running or hiking causes it to develop gradually over days.
Most subungual hematomas are more alarming to look at than they are dangerous. The blood stays trapped under the nail, and as the nail grows out over weeks to months, the dark spot moves toward the tip and eventually disappears. If the pressure under the nail is painful and the injury is recent, a doctor can drain the blood by making a small hole in the nail, which usually provides immediate relief. The key feature of a trauma-related black toe is that it stays the same size or slowly migrates forward as the nail grows, rather than expanding or changing shape.
Poor Blood Flow and Peripheral Artery Disease
When a toe turns black without any obvious injury, the most concerning possibility is that the tissue is not getting enough blood. Peripheral ischemia, rooted in the lower limbs, is a major risk factor for toe necrosis because the metabolic needs of the tissue are not being met, commonly resulting in pain, ulcers, and gangrene.2PubMed Central. Toe Necrosis, Etiologies and Management, a Case Series The underlying culprit is usually peripheral artery disease, where fatty deposits narrow the arteries supplying the legs and feet. Over time, the reduced blood flow can starve tissue of oxygen, and the affected toe or toes begin to die.
Gangrene is the medical term for this tissue death, and it is a serious complication of peripheral vascular disease.3PubMed Central. Understanding Gangrene in the Context of Peripheral Vascular Disease: Prevalence, Etiology, and Considerations for Amputation-Level Determination Dry gangrene, where the tissue dries out and turns black or dark brown, typically progresses slowly and may not be immediately painful because the nerves in the area have also been damaged by the lack of blood supply. Wet gangrene, on the other hand, involves infection in the dying tissue and is a medical emergency with swelling, oozing, and a foul smell.
Treatment depends on how much blood flow remains and how extensive the damage is. In some patients, procedures like angioplasty or stenting can reopen narrowed arteries. But not everyone is a candidate. In one reported case, a 73-year-old man with coronary artery disease and peripheral vascular disease presented with gangrenous toes, but testing revealed multi-segment disease that made both angioplasty and surgical bypass unsuitable. He was treated with blood-thinning medications while his dry gangrenous toes were monitored closely.2PubMed Central. Toe Necrosis, Etiologies and Management, a Case Series In the worst scenarios, amputation of the affected toe or part of the foot becomes necessary to prevent the spread of infection or tissue death.
Blue Toe Syndrome
Sometimes a toe turns blue or black quite suddenly even when the major arteries in the leg seem relatively healthy. Blue toe syndrome is caused by tiny cholesterol crystals that break loose from fatty plaques in larger arteries and travel downstream until they lodge in the small vessels of the toes.4PubMed Central. Blue toe syndrome – systemic cholesterol crystal embolism secondary to cardiovascular procedures: a forensic autopsy report of two cases The blockage cuts off blood flow to a very localized area, turning one or two toes dark while the rest of the foot looks normal and the foot pulses may still be present. This makes it tricky to diagnose because the usual markers of widespread artery disease can appear absent.
Blue toe syndrome can happen spontaneously, but it sometimes follows cardiovascular procedures like catheterization or vascular surgery, which can dislodge plaque material. In at least one published case, a 58-year-old man developed recurrent distal thromboembolism from complex aortic plaques even without classic peripheral artery disease.5PubMed Central. Complex Aortic Plaques and Polycythemia Vera Presenting as Blue Toe Syndrome Without Peripheral Arterial Disease If you notice a single toe suddenly turning purple or black and you have risk factors like high cholesterol or a recent heart procedure, this possibility deserves urgent attention.
Raynaud’s Phenomenon
Raynaud’s phenomenon is a different kind of circulation problem. Rather than a permanent blockage, the small blood vessels in the fingers and toes go into temporary spasm, usually triggered by cold temperatures or emotional stress.6PubMed Central. Raynaud’s Phenomenon: A Current Update on Pathogenesis, Diagnostic Workup, and Treatment During an episode, the affected digits turn white as blood flow stops, then blue as oxygen is depleted, and finally red as circulation returns. How common Raynaud’s is depends partly on the climate, but it affects a meaningful portion of the population in colder regions.7PubMed. Raynaud’s phenomenon and related vasospastic disorders
In its primary form, Raynaud’s is uncomfortable but generally harmless. The episodes come and go, and the toes return to their normal color once they warm up. Secondary Raynaud’s, which occurs alongside autoimmune diseases like scleroderma or lupus, is more dangerous. The vasospasms can be severe enough to cause lasting tissue damage, and in extreme cases the toes may develop persistent darkening or even necrosis.6PubMed Central. Raynaud’s Phenomenon: A Current Update on Pathogenesis, Diagnostic Workup, and Treatment There have also been case reports linking severe Raynaud’s episodes to viral infections. In one case, an 80-year-old man developed intense cyanosis and pain in his digits after a mild COVID-19 infection, ultimately requiring amputation.8PubMed Central. Digit Amputation Secondary to COVID-19-Induced Raynaud’s Phenomenon That outcome is rare, but it illustrates why persistent or worsening color changes in someone with Raynaud’s should not be dismissed.
Diabetes and Foot Complications
Diabetes is one of the biggest risk multipliers for a blackened toe. The disease damages blood vessels and nerves over time, and the combination is particularly dangerous in the feet. Narrowed arteries reduce blood supply, just like in peripheral artery disease, but the added nerve damage means you may not feel the early warning signs of a wound, blister, or pressure injury. By the time the toe looks visibly dark, the tissue may already be significantly compromised.
Because the feet are the farthest point from the heart and already receive less blood flow, they are especially vulnerable. People with diabetes are more likely to develop infections in even minor foot wounds, and those infections can spread rapidly in tissue that is already oxygen-starved. This cascade from poor circulation to unnoticed injury to infection to gangrene is the reason foot complications remain a leading cause of amputation in people with diabetes. Daily foot checks, well-fitting shoes, and prompt attention to any discoloration or wound are standard prevention advice from virtually every diabetes care guideline.
Frostbite and Cold Injury
Prolonged exposure to freezing temperatures can damage tissue directly. Toes are among the first body parts affected because they are small, far from the body’s core, and often inadequately insulated. In the initial stages, frostbitten toes look white or waxy and feel numb. The more serious damage happens in two phases: first, ice crystals form inside the cells and destroy them; second, when the tissue rewarms, an inflammatory and prothrombotic response kicks in that can cause additional injury.9PubMed Central. Frostbite: diagnosis, treatment, prognosis, and future directions
Severe frostbite can leave toes black and hard, closely resembling dry gangrene. In fact, the tissue is gangrenous at that point. One of the frustrating aspects of frostbite treatment is that it can take weeks before doctors can tell exactly how much tissue has been permanently lost versus how much might recover. The guideline often quoted in emergency medicine circles is “frostbite in January, amputate in June,” reflecting the long observation period needed before making irreversible surgical decisions. If you have been exposed to extreme cold and notice your toes turning dark, get medical help immediately. Rapid, controlled rewarming is the first-line treatment, and it should ideally happen under medical supervision.
Fungal Infections and Dark Nails
Not every black toenail involves tissue damage. Certain fungal infections can produce dark pigment that discolors the nail itself, making it look black or streaked with dark bands. Onychomycosis, the medical term for a fungal nail infection, is usually caused by dermatophytes, but non-dermatophyte molds and yeast (Candida) can also be responsible.10PubMed Central. Fungal Melanonychia as a Solitary Black Linear Vertical Nail Plate Streak: Case Report and Literature Review of Candida-Associated Longitudinal Melanonychia Striata Although rare, a Candida infection can produce a longitudinal black streak running the length of the nail that looks quite alarming.
Fungal-related darkening tends to come with other signs of nail infection: thickening, crumbling, lifting of the nail from the nail bed, and sometimes an unpleasant odor. The nail itself is damaged, not the toe beneath it. Treatment typically involves antifungal medications, either topical or oral depending on severity. The important thing is that a dark nail streak from a fungal infection needs to be distinguished from melanoma, which can also present as a dark line on the nail. A dermatologist can usually tell the difference with a careful examination, and if there is any doubt, a biopsy settles the question.
Subungual Melanoma
This is the possibility that worries people the most, and for good reason. Subungual melanoma is a form of skin cancer that originates under the nail. It often appears as a dark brown or black streak running lengthwise along the nail and can be easy to mistake for a bruise or fungal infection early on. One of the most important warning signs is called Hutchinson’s sign, where dark pigment extends beyond the nail itself onto the surrounding skin folds.11PubMed. Hutchinson’s sign: a reappraisal This spreading pigment strongly suggests melanoma, though it is not a guarantee. Some benign conditions can mimic the appearance, and conversely, some melanomas do not produce Hutchinson’s sign at all.
Accurately telling malignant nail pigmentation apart from benign causes, including fungal infections, trauma-related pigment changes, and drug-induced discoloration, is a genuine clinical challenge.12PubMed Central. Challenges in the Diagnosis and Management of Nail Melanocytic Disorders Subungual melanoma is rare compared to other causes of a black toe, but it is disproportionately dangerous because it tends to be diagnosed late. People assume they bruised the nail and wait months for it to grow out, losing valuable time. If you have a dark streak under your toenail that is not growing out with the nail, is widening, or involves pigment on the skin around the nail, get it evaluated by a dermatologist sooner rather than later. Hutchinson’s sign is among the recognized criteria used in diagnosing subungual melanoma.13PubMed. Clinical features of subungual melanoma according to the extent of Hutchinson’s nail sign: a retrospective single-centre study
Less Common Vascular and Systemic Causes
Beyond the more familiar culprits, several rarer conditions can cause blackened toes. Buerger’s disease (thromboangiitis obliterans) is an inflammatory condition of small and medium blood vessels that is strongly linked to tobacco use. Unlike typical peripheral artery disease, which involves fatty plaque buildup, Buerger’s disease causes inflammation and clotting inside the vessel walls, leading to reduced blood flow in the hands and feet.14PubMed Central. Thromboangiitis obliterans (Buerger disease) It tends to affect younger adults who smoke, and the most effective treatment is quitting tobacco entirely. If blood flow has been compromised enough to blacken a toe, the tissue damage may already be permanent.
Calciphylaxis is another rare but devastating condition, seen most often in people with advanced kidney disease. It involves calcification and clotting of small arteries in the skin, which leads to painful, necrotic wounds.15PubMed Central. Calciphylaxis: A Mimic of Vasculitis The mortality rate is high, and the condition can mimic vasculitis or other inflammatory diseases, making diagnosis difficult.16PubMed Central. Calciphylaxis and its co-occurrence with connective tissue diseases While calciphylaxis more commonly affects the thighs and abdomen, it can involve the toes as well. Anyone on dialysis or with severe kidney disease who develops unexplained dark, painful skin lesions on the extremities should be evaluated for this condition urgently.
Other documented causes of toe necrosis include pharmacological sensitivity (reactions to certain medications, particularly vasoconstrictive drugs), cancer-related processes, and granulomatous diseases.2PubMed Central. Toe Necrosis, Etiologies and Management, a Case Series These are uncommon enough that they tend to be diagnosed only after the more likely possibilities have been ruled out.
When You Need a Doctor and How Urgently
Not every black toe requires an emergency room visit, but some do. Here is a rough guide to urgency:
- Same day or emergency: The toe turned black suddenly, is extremely painful, feels cold, and the pain is getting worse. You have swelling, warmth, oozing, or a foul smell suggesting wet gangrene or serious infection. You are experiencing fever or chills alongside the color change. You recently had a heart or vascular procedure and noticed a sudden blue-black toe.
- Within a few days: The discoloration appeared without any known injury and is not improving. You have diabetes, kidney disease, or known peripheral artery disease and notice any new color change in your feet. You have Raynaud’s and the episode is lasting longer than usual or the color is not coming back.
- Scheduled appointment: You are fairly sure you stubbed or bruised the toe, but the dark area is not growing out with the nail after several weeks. A dark streak has appeared under the nail without any injury you can recall. A nail looks thickened, crumbly, and discolored, suggesting a fungal problem.
The overarching principle is straightforward: if there is any chance the blackening involves dying tissue rather than just trapped blood or pigment, err on the side of getting seen quickly. People with diabetes deserve special mention here because they may not feel pain in a compromised toe due to nerve damage, which means the absence of pain is not reassuring the way it would be for someone with healthy sensation.
How Doctors Evaluate a Blackened Toe
The diagnostic workup depends on what the doctor suspects. For a straightforward subungual hematoma, a physical exam is usually enough. For suspected vascular problems, the evaluation typically starts with checking the pulses in the foot and ankle, then moves to imaging. Doppler ultrasound is the standard first test for assessing blood flow in the legs. In more complex cases, angiography can map out exactly where arteries are blocked or narrowed.
Newer noninvasive tools are also entering clinical use. Transcutaneous oxygen pressure measurement, which gauges how much oxygen is reaching the skin, and infrared thermography, which maps skin temperature as a proxy for blood flow, have both shown promise in evaluating lower-limb perfusion.17PubMed Central. The correlation between transcutaneous oxygen pressure (TcPO(2)) and forward-looking infrared (FLIR) thermography in the evaluation of lower extremity perfusion according to angiosome These tools help doctors decide how likely tissue is to heal on its own versus needing intervention.
If melanoma is a concern, dermatoscopy (a specialized magnified examination of the nail) is the first step, followed by a biopsy if the appearance is suspicious. For fungal infections, a clipping of the nail can be sent to a lab for culture. Blood tests can identify markers of autoimmune disease, clotting disorders, or kidney dysfunction that might point to rarer systemic causes like Buerger’s disease or calciphylaxis. The variety of possible causes is exactly why a black toe that does not have an obvious explanation should be evaluated rather than assumed to be harmless.
Medication-Related Discoloration
Certain medications can darken toenails without any underlying tissue damage. Chemotherapy drugs are the best-known offenders, with several agents capable of producing brown or black bands across multiple nails. Some antibiotics, antimalarial drugs, and antiretroviral medications can do the same. The discoloration is cosmetic and typically reverses once the medication is stopped, though it may take many months for the affected nail to grow out completely.
This type of drug-induced darkening is easy to confuse with melanoma or fungal melanonychia, which is one reason doctors ask about your medication list when evaluating a dark nail. If you started a new medication in the months before the discoloration appeared and multiple nails are affected symmetrically, the drug is the most likely explanation. Still, any dark nail streak that appeared alongside a new medication should be confirmed as drug-related rather than simply assumed to be, because melanoma does not care about the timing of your prescriptions.