A dark appearance on a toe can be concerning, but causes range widely from a simple bruise to conditions requiring immediate medical intervention. The discoloration is a symptom, and understanding its underlying source is the first step toward appropriate care. The color change can affect the skin, nail, or the area underneath, presenting as shades of red, purple, brown, or black. Determining the exact nature of the discoloration involves considering recent activity, systemic health, and the specific visual characteristics of the area.
Physical Causes: Bruising, Friction, and Hematomas
The most frequent cause of a dark toe is physical trauma, resulting in bleeding beneath the nail plate or within the soft tissue. A subungual hematoma occurs when blunt force or repetitive pressure damages small blood vessels in the nail bed, causing blood to pool under the nail.
The trapped blood initially appears reddish-purple and then turns dark brown or black as it clots and oxidizes. This pooling can cause throbbing pain due to pressure buildup, often relieved by a medical professional draining the blood (trephination). If the hematoma is small and not causing severe pain, the discoloration will slowly grow out with the nail.
Friction from footwear can also cause discoloration without an acute injury. Chronic rubbing can trigger post-inflammatory hyperpigmentation, increasing melanin production in the skin and resulting in diffuse darkening or brown patches. This darkening is generally harmless but signals the need to address the source of the mechanical irritation.
Vascular Causes: Restricted Blood Flow and Ischemia
A dark or bluish toe not resulting from trauma can indicate a problem with blood circulation. The bluish hue, known as cyanosis, is caused by a lack of oxygenated blood reaching the tissues; hemoglobin turns darker when oxygen-depleted.
Peripheral Artery Disease (PAD) is a condition where plaque buildup narrows the arteries, restricting blood flow to the extremities. Severe PAD can lead to critical limb ischemia, where the lack of oxygen and nutrients causes intense pain, numbness, and ultimately, tissue death (gangrene), which appears black. This darkening represents an urgent medical condition as cells are deprived of oxygen.
Another vascular cause is Raynaud’s phenomenon, where small arteries temporarily narrow in response to cold or stress. This vasospasm causes the toe to turn white, then blue (cyanotic), and finally red as blood flow returns. While often episodic and manageable, persistent or severe cyanosis, especially if accompanied by pain or ulceration, warrants immediate evaluation.
Dermatological Causes: Fungal Infections and Pigment Changes
Discoloration can also originate in the nail or skin due to infections or cellular changes. Fungal infections of the nail (onychomycosis) are common and can cause the nail to turn various colors, including white, yellow, green, or dark brown to black. The dark color may be due to the fungus or debris trapped beneath the nail, often accompanied by thickening, crumbling, or lifting of the nail plate.
A less common but serious cause of darkening is acral lentiginous melanoma (ALM), a form of skin cancer developing under the toenail. ALM typically appears as a dark longitudinal streak running the length of a single nail (melanonychia). Unlike a bruise, this dark band will not grow out with the nail.
Warning signs include the pigment spreading to the surrounding skin (Hutchinson’s sign) or the streak being wider than three millimeters with irregular borders. This type of melanoma is often diagnosed late because it is mistaken for a bruise or fungal infection. The prognosis of ALM depends heavily on early detection.
Recognizing Urgent Symptoms and Seeking Care
While minor trauma and friction-related discoloration can be managed, certain signs indicate the need for immediate medical attention. Acute changes in color accompanied by severe, sudden pain or profound numbness are red flags for acute limb ischemia, where blood flow is completely blocked. A toe that feels unusually cold to the touch, or where the pulse is difficult to find, requires emergency evaluation to preserve the limb.
Signs of a spreading infection also demand prompt care, including increasing redness or streaking, significant swelling, or the presence of pus or foul-smelling drainage. For issues under the nail, a dark area that is rapidly changing size, is accompanied by a painful nodule, or a dark streak that expands to involve the surrounding skin should be a primary concern.
Consulting a podiatrist or primary care provider is appropriate for persistent, non-urgent discoloration. However, the presence of severe pain, coldness, or signs of acute infection warrants a visit to the emergency department.