✅ Medically reviewed by Dr. Thomas Biernacki, DPM — Board-Certified Podiatrist · Last updated April 7, 2026
Medically reviewed by Dr. Carl Jay, DPM · Board-Certified Podiatrist · Balance Foot & Ankle · Updated April 2026
⚡ Quick Answer
A black spot under your toenail is most commonly a subungual hematoma (blood trapped under the nail from trauma) or a benign melanocytic streak. However, it can also be a sign of subungual melanoma — a rare but serious form of skin cancer. Any new, dark discoloration under a toenail that wasn’t caused by obvious injury should be evaluated by a podiatrist or dermatologist.
📋 Table of Contents
Common Causes of a Black Spot Under the Toenail
Discovering a dark spot under your toenail can be alarming, but in most cases the cause is benign. The key is knowing which features are harmless and which deserve professional attention. Here are the most common causes, from most likely to least likely.
Subungual Hematoma (Bruise Under the Nail)
This is by far the most common cause of a black toenail. A subungual hematoma forms when blood collects between the nail plate and the nail bed after trauma — dropping something on the toe, stubbing it, or repetitive pressure from shoes that are too tight (a condition runners call “black toenail” or “jogger’s toe”). The discoloration ranges from dark red to purple to black.
Key features of a subungual hematoma: the dark area usually doesn’t extend to the cuticle, it’s associated with a specific injury or activity, it may be painful initially, and it gradually grows out with the nail over 6–12 months. The blood doesn’t change shape or spread — it simply moves forward as the nail grows. If the hematoma covers more than 25% of the nail area or is extremely painful, your podiatrist can drain it (trephination) for immediate relief.
Melanonychia — A Pigmented Streak in the Nail
Melanonychia is a longitudinal dark band running from the cuticle to the tip of the nail, caused by increased melanin production in the nail matrix. It’s extremely common in people with darker skin tones — studies show that nearly 100% of African Americans over age 50 have at least one pigmented nail streak. In lighter-skinned individuals, melanonychia is less common and warrants closer monitoring.
Benign melanonychia is typically uniform in color and width, present in multiple nails, stable over time, and has clearly defined borders. However, because melanonychia can also be the earliest sign of subungual melanoma, any new single-nail streak — particularly in lighter-skinned patients — should be evaluated professionally.
Subungual Melanoma — The Serious Concern
Subungual melanoma is rare (about 0.7–3.5% of all melanomas), but it’s the most important diagnosis to rule out when evaluating a dark toenail spot. It develops from melanocytes in the nail matrix and can be life-threatening if caught late. The big toe is the most commonly affected.
The ABCDEF rule helps identify concerning features: Age (peak incidence 50–70, or any age in high-risk patients), Band (brown-black band wider than 3mm), Change (rapid widening or color change), Digit (most common on the thumb or big toe), Extension of pigment onto the cuticle or skin fold (Hutchinson’s sign — a critical warning sign), and Family history of melanoma.
Subungual melanoma is frequently diagnosed late because it’s often mistaken for a bruise or fungal infection. This delay reduces survival rates significantly. When caught early (before invasion into deeper tissues), the prognosis is excellent. This is why any unexplained, persistent dark nail discoloration should be evaluated — the downside of getting it checked is minimal, while the cost of missing it can be severe.
Fungal Infection
While most fungal toenail infections cause yellowing or whitening, certain fungal strains (particularly molds) can produce dark pigmentation. Dark fungal infections are more common in tropical climates but can occur anywhere. Unlike melanoma, fungal discoloration typically involves multiple nails, is associated with nail thickening and crumbling, and may respond to antifungal treatment. A nail clipping can be sent for culture to confirm the diagnosis. For comprehensive fungal nail information, see our toenail fungus treatment guide.
How a Black Toenail Spot Is Diagnosed
At Balance Foot & Ankle, your podiatrist will take a detailed history (trauma, onset, progression, symptoms) and examine the nail with dermoscopy — a specialized magnifying device that reveals patterns invisible to the naked eye. Dermoscopy can often distinguish a benign hematoma or melanonychia from a suspicious lesion without the need for biopsy.
If melanoma is suspected, a nail matrix biopsy is the gold standard — a small tissue sample is taken from the growth center of the nail and sent for pathological examination. Nail clippings may be sent for fungal culture if infection is suspected. Serial photography (documenting the spot over time) is useful for monitoring stable-appearing melanonychia.
Treatment Options
Treatment depends entirely on the diagnosis. Subungual hematomas can be observed (the blood grows out naturally over months) or drained if painful. Melanonychia that is confirmed benign requires only periodic monitoring. Fungal infections are treated with antifungal medications. Subungual melanoma requires prompt surgical excision — the extent of surgery depends on the depth and stage of the melanoma, and may involve referral to an oncologic surgeon.
⚠️ When to See a Podiatrist — Don’t Delay
- Any new dark streak or spot that wasn’t caused by obvious trauma
- A dark band that is widening, changing color, or has blurry borders
- Dark pigment extending onto the cuticle or surrounding skin (Hutchinson’s sign)
- A dark spot that hasn’t grown out after 6–12 months
- Nail destruction or deformity accompanying the discoloration
- Any dark nail lesion in a person over 50 or with melanoma risk factors
Dr. Tom Biernacki, DPM is a double board-certified podiatrist and foot & ankle surgeon at Balance Foot & Ankle Specialists in Southeast Michigan. With over a decade of clinical experience, he specializes in heel pain, bunions, diabetic foot care, sports injuries, and minimally invasive surgery. Dr. Biernacki is a member of the APMA and ACFAS, and his patient education content on MichiganFootDoctors.com and YouTube has reached over one million views.
- Diagnosis and Treatment of Plantar Fasciitis (PubMed / AAFP)
- Heel Pain (APMA)
- Hallux Valgus (Bunions): Evaluation and Management (PubMed)
- Bunions (Mayo Clinic)
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