Toenail Discoloration: Causes, Colors & Treatment

Nail Color	Most Common Cause	Other Causes	Action
Yellow / thickened	Onychomycosis (toenail fungus)	Yellow nail syndrome, nail polish, psoriasis	Culture/PAS stain to confirm; antifungal if positive
Black / dark brown (post-trauma)	Subungual hematoma	Melanocytic nevus, melanoma	Monitor — if not growing out in 2–3 months, biopsy
Black / brown (no trauma)	Subungual melanoma — URGENT	Fungal melanonychia, medications	Urgent podiatry/dermatology — biopsy
White (entire nail)	Terry’s nails (liver disease, heart failure)	Onychomycosis (white superficial), trauma	Systemic evaluation if no trauma history
White spots / patches	Leukonychia punctata (trauma to matrix)	Zinc deficiency, fungal (white superficial)	Usually benign — grows out; check zinc if multiple nails
Green / black-green	Pseudomonas bacterial infection	Aspergillus fungal infection	Topical antibiotic drops; partial nail debridement
Blue / blue-gray	Hypoxia, medications (antimalarials, minocycline)	Wilson’s disease, silver (argyria)	Cardiac/pulmonary evaluation; medication review
Red streaks (splinter hemorrhages)	Trauma (most common)	Endocarditis, vasculitis, psoriasis	Multiple nails + fever = cardiac evaluation

Toenail Fungus Severity	ONYCHOSIS Score	Nail Area Affected	Preferred Treatment
Mild	1–5	<25% of nail surface	Topical antifungal: tavaborole, efinaconazole, ciclopirox (12–48 weeks)
Moderate	6–15	25–75% of nail surface	Oral terbinafine 250mg x12 weeks (first-line); or itraconazole pulse x3 months
Severe	16–28	>75% of nail surface	Oral terbinafine + laser adjunct; consider partial/total nail avulsion
Dermatophytoma (yellow streak)	Variable	Dense central fungal colony	Oral antifungal + nail debridement; laser; nail avulsion if refractory

Quick answer: Toenail Discoloration is a common nail condition with multiple causes including trauma, fungal infection, biomechanical pressure, and underlying medical conditions. Treatment depends on the cause: trauma resolves as the nail grows out (6-12 months), fungus needs antifungal therapy, and biomechanical issues need shoe and orthotic correction. Call (810) 206-1402.

Diagnosing Toenail Discoloration by Color

The color and distribution of toenail discoloration is the first diagnostic clue — before any test is ordered. Different pathological processes produce characteristic color patterns that, combined with the clinical history and nail examination, guide the workup efficiently. In our clinic, we use a systematic color-based approach to evaluate every discolored toenail: the vast majority are fungal, a meaningful proportion are traumatic hematomas, and a small but critical fraction are conditions — including melanoma — that have life-changing diagnostic implications if missed.

Yellow or Yellow-Brown Toenails — Onychomycosis

Yellow to yellow-brown toenail discoloration is the signature presentation of onychomycosis (toenail fungal infection) and accounts for approximately 90% of all abnormally colored toenails in adults. The discoloration typically starts at the distal free edge (distal subungual onychomycosis — the most common pattern) and progresses proximally as the infection advances beneath the nail plate. It is accompanied by nail thickening, subungual hyperkeratosis (chalky buildup under the nail), and eventually nail plate crumbling and onycholysis (nail plate separation). The hallux is most commonly affected because it has the slowest nail growth and the most trauma exposure. Confirmation requires nail clipping for KOH preparation and fungal culture — clinical appearance alone misses the diagnosis in up to 30% of cases (other conditions mimic onychomycosis, and empiric oral antifungals are not appropriate without confirmation).

Yellow nail syndrome is a rare condition producing slow-growing, thickened, transversely curved yellow nails on all digits — associated with lymphedema and respiratory disease. It is distinguished from onychomycosis by the symmetrical all-nail involvement, absence of subungual debris, and negative fungal culture. Yellow discoloration can also result from prolonged nail polish use (the dye stains the nail plate) — this clears with nail growth after stopping polish use.

Black Toenails — Subungual Hematoma and Melanoma

Black toenail discoloration has two dominant causes with very different clinical significance: subungual hematoma (blood under the nail from trauma) and subungual melanoma (malignant melanoma of the nail unit). Subungual hematoma is dramatically more common and in runners is nearly universal — repetitive nail-tip impact in the toe box causes bleeding under the nail that appears as a dark red-black discoloration, often painful at onset. It grows distally with the nail and clears completely as it reaches the free edge and is trimmed away. The diagnosis is confirmed by the history (recent trauma or increased running) and the observation that the discoloration moves forward with nail growth over weeks to months.

Subungual melanoma (acral lentiginous melanoma) is the critical diagnosis not to miss. It presents as a brown-black longitudinal stripe (melanonychia striata) running along the length of the nail from the matrix to the free edge — or as diffuse darkening of the nail plate. The warning signs that distinguish melanoma from benign melanonychia include: the stripe is wider than 3 mm, the stripe has irregular borders or color variation (darker in the center, lighter at edges), the stripe bleeds beyond the nail fold (Hutchinson’s sign), the nail has changed over months without a clear traumatic cause, and the patient is an adult over 50. Subungual melanoma is disproportionately common in patients of color, who have a higher rate of acral melanoma relative to other melanoma subtypes. Any suspicious nail stripe requires dermatology or podiatric surgery referral for biopsy — nail matrix biopsy under digital block anesthesia confirms or excludes the diagnosis.

Green Toenails — Pseudomonas Infection

Green toenail discoloration indicates Pseudomonas aeruginosa bacterial infection of the nail bed — a gram-negative rod that produces the pigment pyocyanin, which stains the nail green. Pseudomonas infection occurs most commonly under a nail that has been lifted from the nail bed (onycholysis) — the gap between the separated nail plate and the nail bed creates the warm, moist environment the bacteria colonize. It frequently complicates onychomycosis (the fungal infection creates onycholysis, which then gets secondarily colonized by Pseudomonas). Treatment requires removing the separated nail plate (clipping it back to the point of firm attachment), cleaning the nail bed with dilute bleach solution (1:10 sodium hypochlorite) or acetic acid (white vinegar), and applying topical ciprofloxacin otic solution. Oral antibiotics are rarely required for localized nail Pseudomonas. The green color resolves as the infection clears and the nail regrows.

White Toenails — Leukonychia and Superficial White Onychomycosis

White toenail discoloration encompasses several distinct entities. Leukonychia punctata (discrete white spots) is the most common — caused by minor trauma to the nail matrix and entirely benign, moving distally with nail growth. Superficial white onychomycosis (SWO) is a fungal infection limited to the dorsal nail plate surface that produces white chalky patches that can be physically scraped off — unlike true leukonychia which cannot. Terry’s nails (proximal two-thirds white, distal pink band) and Lindsay’s nails (proximal half white, distal half brown-red) are apparent leukonychia from nail bed vascular changes associated with liver cirrhosis and chronic renal disease respectively — these do not move with nail growth. Total white nails on all digits warrant systemic evaluation for hypoalbuminemia, liver disease, or renal failure.

Brown Toenails — Differential Diagnosis

Brown toenail discoloration has a broader differential than other colors. Causes include: advanced onychomycosis (yellow transitions to brown as infection progresses), subungual hematoma resolving from black to brown, drug-induced nail pigmentation (tetracyclines, antimalarials, chemotherapy agents, AZT), tobacco staining, exogenous dye contamination (shoe dye, nail polish), and longitudinal melanonychia from benign lentigo or melanocytic nevus of the nail matrix. A single brown longitudinal streak that is widening, irregular, or accompanied by pigmentation of the surrounding skin (Hutchinson’s sign) requires biopsy regardless of the patient’s clinical history or reassurances — subungual melanoma carries a significantly worse prognosis when diagnosed late.

When to Biopsy a Toenail

Nail matrix biopsy is indicated when a discolored toenail does not fit the typical pattern of a benign diagnosis or when a diagnosis with serious implications (melanoma) cannot be excluded on clinical grounds. Biopsy indications include: any new brown-black longitudinal stripe in an adult, particularly if wider than 3 mm or with irregular color variation; a nail stripe that has changed in width, color, or distribution over months; Hutchinson’s sign (pigmentation spreading to the periungual skin); a discolored nail that fails to clear with appropriate antifungal treatment; and any nail change with a personal or family history of melanoma. Nail matrix biopsy is performed under digital block anesthesia as an office procedure and is not painful when properly anesthetized.

Not ideal for: Active nail infections or open nail bed wounds. PowerStep Pinnacle insoles reduce toe box pressure and repetitive nail trauma — the primary cause of subungual hematoma in runners and the contributing factor for onycholysis that leads to green nail Pseudomonas infection.

Not ideal for: Open nail wounds. Doctor Hoy’s natural arnica gel is appropriate for the periungual bruising, soreness, and soft tissue tenderness around traumatic nail changes with intact skin.

Frequently Asked Questions

What causes yellow toenails

Yellow toenails are caused by onychomycosis (fungal nail infection) in the vast majority of cases — approximately 90% of yellow or yellow-brown discolored nails in adults. The infection starts at the free edge and advances proximally, accompanied by nail thickening and subungual debris. Other causes include yellow nail syndrome (all nails, associated with lymphedema and lung disease), prolonged nail polish use (dye staining that clears with nail growth), and psoriasis (which can produce yellow-brown oil drop sign beneath the nail plate). Definitive diagnosis of onychomycosis requires nail clipping for KOH and culture — empiric oral antifungal treatment without culture confirmation is not appropriate.

Is a black toenail a sign of cancer

Most black toenails are subungual hematomas from trauma — blood pooled under the nail that appears dark red-black. A traumatic hematoma moves forward with nail growth and clears completely over 3-6 months. Subungual melanoma (a form of skin cancer) also presents as black or dark brown nail discoloration — but critically, it does not move with nail growth. The clinical test is observation: if the discoloration is shifting distally as the nail grows over 4-8 weeks, it is a healing hematoma. If it stays in the same position while the nail grows forward, it requires biopsy. A longitudinal stripe that extends from the base to the free edge, is widening, has irregular borders, or is accompanied by pigmentation spreading onto the surrounding skin (Hutchinson’s sign) requires urgent evaluation regardless of history.

How do you treat green toenails

Green toenails from Pseudomonas infection are treated by removing the lifted or separated nail plate back to the point of firm attachment (exposing the infected nail bed), soaking the nail in dilute white vinegar (1:1 ratio with water) for 15 minutes daily, and applying topical ciprofloxacin otic solution to the nail bed if available — or continuing the vinegar soaks, which create an acid environment inhospitable to Pseudomonas. Antifungal treatment alone does not treat Pseudomonas — the bacterial infection requires antibacterial treatment. Oral antibiotics are rarely needed for localized disease. The green color resolves as the infected nail bed clears and the new nail plate grows in.

The Bottom Line

Toenail discoloration is common and usually benign — yellow-brown nails from onychomycosis, black nails from shoe trauma, white spots from minor nail matrix injury. The diagnostic framework is simple: color guides the differential, and the key question for any dark nail is whether the discoloration moves distally with nail growth (hematoma) or stays fixed (melanoma, requires biopsy). If you have a nail stripe that has not moved in 4-6 weeks, a green nail that hasn’t cleared, or any nail change in a diabetic patient, a podiatric evaluation will sort out the cause quickly and definitively. The nails provide a window into both local foot problems and systemic health — they are worth taking seriously.

Sources

1. Tosti A, et al. “Subungual melanoma: clinical, dermoscopic, and pathologic features in 70 cases.” J Am Acad Dermatol. 2011.
2. Piraccini BM, Alessandrini A. “Onychomycosis: a review.” J Fungi (Basel). 2015.
3. Iorizzo M, et al. “Subungual hematoma.” J Am Acad Dermatol. 2009.
4. Fawcett RS, et al. “Nail abnormalities: clues to systemic disease.” Am Fam Physician. 2004.
5. Haneke E. “Nail surgery.” Clin Dermatol. 2013.

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