Dark Streak in Toenail: Subungual Melanoma vs Hematoma Michigan | DPM

Medically reviewed by Dr. Tom Biernacki, DPM — Board-Certified Podiatric Surgeon — Balance Foot & Ankle, Howell & Bloomfield Hills, MI. Last updated April 2026.

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A dark brown or black streak running lengthwise under a toenail must always be evaluated by a podiatrist or dermatologist — it can represent a benign blood collection (subungual hematoma) or one of the most dangerous skin cancers, subungual melanoma. Dr. Tom Biernacki, DPM, at Balance Foot & Ankle in Howell and Bloomfield Hills, Michigan, evaluates all nail pigmentation changes and performs nail biopsy when indicated.

Quick Answer: When Is a Dark Toenail Streak Dangerous?

A dark streak (melanonychia) under a toenail is concerning for subungual melanoma when: it appears without any recalled injury; it is getting wider over weeks or months; it has irregular borders or multiple colors; it extends from the nail onto the surrounding skin (Hutchinson’s sign); or it occurs in a patient over age 50. A dark area that appeared after a clear injury (dropped object, stubbed toe, running descent) and is moving distally with nail growth over 3–4 months is almost always a subungual hematoma (benign). Any ambiguous case requires same-day podiatric or dermatologic evaluation — subungual melanoma delays in diagnosis average 2 years nationally, and stage at diagnosis determines survival.

What Is Melanonychia (Dark Nail Streaks)?

Melanonychia refers to brown or black pigmentation of the nail plate, arising from melanin deposits in the nail matrix or nail bed. It is classified as melanonychia striata (a longitudinal band, the concerning type) or diffuse melanonychia (the entire nail, more commonly benign). Longitudinal melanonychia has many causes: melanocytic activation (common and benign, especially in darker-skinned individuals), melanocytic nevus (a mole in the nail matrix), subungual melanoma (the diagnosis not to miss), nail trauma with hematoma, medications (hydroxychloroquine, AZT, some chemotherapy agents), and systemic conditions (Addison’s disease, HIV). In Fitzpatrick skin types V–VI (darker skin tones), longitudinal melanonychia is often benign melanocyte activation — but it still requires evaluation to exclude melanoma.

Subungual Hematoma: The Common Benign Cause

Subungual hematoma — blood pooling under the nail from trauma — is by far the most common cause of a dark toenail. It is uniformly dark (blue-black), appears within hours to days of a specific traumatic event, and moves distally (toward the nail tip) at the rate of nail growth — approximately 1–2mm per month for toenails. A hematoma that first appeared 3 months ago should be 3–6mm from its original position and well on its way to the nail tip. Painful subungual hematomas occupying more than 50% of the nail plate benefit from trephination (small hole drilled through the nail to decompress the blood) — this provides immediate relief and prevents nail loss from pressure necrosis. Painless hematomas are watched until they grow out.

Subungual Melanoma: The Diagnosis Not to Miss

Subungual melanoma is a rare but deadly form of melanoma arising from melanocytes in the nail matrix or nail bed. It accounts for approximately 1–3% of all melanomas in the general US population but represents a disproportionate percentage of melanomas in darker-skinned individuals (up to 40% in Black patients) — where it is particularly likely to be misdiagnosed as a benign finding. The big toe and thumb are the most commonly affected digits. Warning features (ABCD + E criteria for nail melanoma): Age (peak 5th–7th decade); Brown/black color band wider than 3mm; Change in size, shape, or color over time; Digit — the great toe, thumb, or index finger; and Extension of pigment to the surrounding skin (Hutchinson’s sign) — any periungual pigmentation is a red flag requiring urgent biopsy. 5-year survival for early-stage (in situ) subungual melanoma is >95%. 5-year survival for late-stage (with distant metastasis) is approximately 15%.

The ABCDEF Rule for Nail Pigmentation

The ABCDEF mnemonic assists clinical triage of nail pigmentation: Age and race — peak incidence age 50–70; higher risk in darker skin tones. Band — brown/black band of width ≥3mm, with irregular or blurry borders. Change — rapid increase in width or change in pigmentation pattern. Digit — big toe or thumb most commonly; single digit involvement. Extension — Hutchinson’s sign (pigment spreading to periungual skin). Family or personal history — prior melanoma or family history of melanoma. Three or more of these criteria warrant urgent nail matrix biopsy.

Nail Biopsy: The Definitive Diagnostic Procedure

When clinical evaluation cannot definitively exclude melanoma, nail matrix biopsy is indicated. The procedure is performed under digital block anesthesia — the nail plate is partially or fully avulsed to expose the nail matrix, and a 3mm punch biopsy is taken from the pigmented matrix area. The specimen is sent for dermatopathologic analysis with melanocytic immunohistochemistry (S100, Melan-A, HMB-45). Results typically return in 7–10 business days. Biopsy-related nail changes (ridge, thinning) are usually transient but permanent changes can occur in 5–10% of cases. The risk of permanent nail change from biopsy is substantially outweighed by the risk of missing a melanoma. In our clinic, we refer all suspected melanonychia cases requiring biopsy to dermatology for joint management and ensure there is no delay in the referral process.

Differential Diagnosis: Other Causes of Nail Discoloration

Other nail color changes that are frequently concerning to patients but are generally benign: White nails (leukonychia) — usually nail plate trauma (true leukonychia, in the nail plate itself) or onychomycosis (white surface changes); Yellow-brown thickened nails — onychomycosis (toenail fungus) confirmed by culture; Green discoloration — pseudomonas bacterial infection, typically under a lifted nail plate; Yellow dystrophic nails — yellow nail syndrome (lymphedema, pleural effusions — systemic evaluation needed); Splinter hemorrhages (tiny dark lines, not a band) — most commonly trauma, also seen in bacterial endocarditis; Red streak under a nail — glomus tumor (rare, highly pressure-tender point, benign but requires excision). Any nail change that has been present more than 4–6 weeks and is not clearly explained by an identified traumatic event should be evaluated by a podiatrist or dermatologist.

Hutchinson’s Sign: The Critical Red Flag

Hutchinson’s sign is the extension of brown or black pigmentation from under the nail onto the periungual skin (the cuticle, the skin folds beside the nail, or the fingertip/toe tip skin). It is pathognomonic (essentially diagnostic) for subungual melanoma when present — the melanoma has invaded beyond the nail matrix into the surrounding dermis. Pseudo-Hutchinson’s sign can occur with benign conditions (ethnic nail pigmentation, benign nevus) where the pigment appears to extend but is actually visible through the translucent cuticle without true skin invasion. True Hutchinson’s sign requires urgent biopsy. Any patient with periungual pigmentation surrounding a dark nail streak should be seen same-day or within 1 week at maximum. Call (810) 206-1402.

Book a Nail Pigmentation Evaluation in Michigan

Dr. Tom Biernacki, DPM, evaluates all nail pigmentation changes and coordinates nail biopsy and dermatology referral when indicated at Balance Foot & Ankle in Howell (4330 E Grand River Ave, Howell MI 48843) and Bloomfield Hills (43494 Woodward Ave #208, Bloomfield Hills MI 48302). Urgent appointments available for Hutchinson’s sign or rapidly changing nail bands. Call (810) 206-1402 or book online →.

Medically reviewed by Dr. Tom Biernacki, DPM — podiatric physician and surgeon, Howell and Bloomfield Hills, Michigan.

Toenail Concerns? See a Podiatrist

A dark streak or discoloration under your toenail should always be evaluated by a podiatrist to rule out subungual melanoma. Early detection is critical for the best outcomes. Our board-certified podiatrists perform thorough nail evaluations and dermoscopy.

Learn About Our Toenail Treatments → | Book Your Appointment | Call (810) 206-1402

Clinical References

1. Levit EK, et al. “The ABC rule for clinical detection of subungual melanoma.” Journal of the American Academy of Dermatology. 2000;42(2):269-274.
2. Braun RP, et al. “Diagnosis of nail melanoma: a review of the literature.” British Journal of Dermatology. 2007;157(S2):9-13.
3. Benati E, et al. “Clinical and dermoscopic features of subungual melanoma.” Dermatology Practical & Conceptual. 2018;8(1):47-54.

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Dr. Tom Biernacki, DPM

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.