Discolored Toenail That’s Not Fungus: Causes

Not every discolored toenail is a fungal infection — a fact that matters clinically because misdiagnosis leads to months of unnecessary antifungal treatment while the actual cause goes untreated. Toenail discoloration occurs whenever the nail plate, nail bed, or subungual space is affected by trauma, systemic disease, medication, benign nail pathology, or — in rare cases — malignancy. The color and pattern of discoloration provide important diagnostic clues: yellow-white thickening with subungual debris suggests onychomycosis; black or dark brown discoloration under the nail raises concern for subungual hematoma or, if there is no injury history, subungual melanoma; white discoloration has a long differential from leukonychia to prior trauma to rare systemic disease; and green discoloration specifically suggests Pseudomonas bacterial colonization, not fungal infection.

At Balance Foot & Ankle in Howell and Bloomfield Township, MI, nail discoloration without confirmed fungal etiology receives proper diagnostic workup before antifungal therapy is initiated — because treating the wrong diagnosis wastes time and exposes patients to drug side effects unnecessarily.

Toenail Discoloration by Color: Non-Fungal Causes

Color	Non-Fungal Causes	Distinguishing Features	Action
Black / dark brown	Subungual hematoma (blood under nail); subungual melanoma; subungual melanocytic nevus; medications (hydroxyurea, minocycline)	Hematoma: history of trauma; moves distally as nail grows; irregular pigment band without trauma history → biopsy	Rule out melanoma if no trauma history or if pigment band has irregular borders (Hutchinson sign = melanoma until proven otherwise)
White (leukonychia)	True leukonychia: nail matrix injury → white spots/bands; apparent leukonychia: nail bed changes (hypoalbuminemia → Terry nails; renal failure → half-and-half nails); air between nail plate and bed	True leukonychia moves with nail growth; apparent leukonychia (nail bed) does not move distally	Systemic white nail: check albumin, BUN/creatinine; isolated white spots: normal, post-traumatic
Green	Pseudomonas aeruginosa colonization of the subungual space (chloronychia)	Green-black color; occurs in previously separated or damaged nail; no fungal elements on culture; Pseudomonas grows on nail culture	Topical antibiotics (gentamicin, ciprofloxacin); keep dry; not antifungal
Yellow (without thickening/debris)	Yellow nail syndrome (lymphatic disease + respiratory disease); psoriasis; onycholysis from trauma or skin condition; nail polish staining	Yellow nail syndrome: thick, slow-growing, no lunula + lymphedema + pleural effusions; psoriasis: pitting + oil-drop sign + skin involvement; nail polish: uniform staining, bilateral, history	Yellow nail syndrome: pulmonology and lymphedema referral; psoriasis: dermatology; polish staining: discontinue polish + base coat
Brown / tan streaks (melanonychia)	Longitudinal melanonychia: normal variant in darker-skinned individuals; melanocytic nevus; drug-induced (doxorubicin, psoralen); Addison disease	Multiple nails = likely drug or systemic; single nail with irregular band, widening, Hutchinson sign → biopsy	Single darkening band in fair-skinned person: low threshold for biopsy to exclude subungual melanoma
Red / hemorrhagic splinters	Splinter hemorrhages: bacterial endocarditis (classic sign); vasculitis; antiphospholipid syndrome; trauma	Splinter hemorrhages at nail bed: multiple nails + fever + cardiac murmur → echocardiogram; isolated splinter = often traumatic	Multiple splinter hemorrhages with systemic symptoms: cardiology/internal medicine

The Critical Exception: When Toenail Discoloration Could Be Melanoma

Subungual melanoma — malignant melanoma arising from the nail matrix — is rare but life-threatening when missed. It typically presents as a longitudinal melanonychia (a dark brown or black streak running from the base to the tip of the nail) that gradually widens or darkens, particularly in a single nail of a fair-skinned adult who has no history of nail trauma. The ABCDEFs of subungual melanoma: Age and race (peak 5th–7th decade; more common in Asian, African, and Hispanic populations); Band (width greater than 3 mm; irregular borders; multiple colors); Change (history of change in a previously stable pigmentation); Digit (thumb, index finger, great toe most commonly); Extension of pigment into the proximal or lateral nail fold skin (Hutchinson sign — pathognomonic of subungual melanoma); and Family history of melanoma. Any nail with features raising concern for melanoma requires biopsy — this cannot be diagnosed clinically and cannot be delayed.

Diagnosing Non-Fungal Nail Discoloration at Balance Foot & Ankle

We evaluate toenail discoloration with fungal culture/PAS staining, clinical nail examination, and nail biopsy when melanoma or lichen planus is suspected at our Howell (4330 E Grand River Ave) and Bloomfield Township (43494 Woodward Ave #208) offices. We do not initiate antifungal treatment without confirmed fungal diagnosis. Call (810) 206-1402 for a nail evaluation.

For a complete clinical overview: Toenail Problems Complete Guide — nail discoloration, ridges, fungus, and injury treated