Toenail Problems Beyond Fungus: 8 Conditions That Affect Nail Health

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

When Toenail Changes Mean More Than Fungus

Discolored, thickened, or abnormal-appearing toenails are often dismissed — or self-treated — as fungal infection. And while onychomycosis (nail fungus) is indeed common, affecting up to 14% of adults in the United States, a wide range of other conditions can produce similar or overlapping nail changes. Applying antifungal treatment to a condition that isn’t fungal wastes time, delays proper treatment, and perpetuates the underlying problem.

Understanding the spectrum of toenail conditions helps patients recognize when professional evaluation is needed and what the podiatrist might be looking for during examination.

1. Onychomycosis (Toenail Fungus)

The most common nail condition, toenail fungus presents with thickening, yellowish or brown discoloration, brittleness, crumbling of the nail edge, and separation of the nail from the underlying nail bed (onycholysis). Caused primarily by dermatophyte fungi (Trichophyton rubrum most commonly), diagnosis is confirmed by nail culture or PAS stain of nail clippings rather than appearance alone. Treatment involves oral antifungal medications (terbinafine is most effective), topical antifungals for mild cases, and newer laser treatments for select patients.

2. Subungual Hematoma (Blood Under the Nail)

A dark red, purple, or black spot under the toenail is most commonly a subungual hematoma — pooled blood from trauma to the nail bed. This occurs after stubbing a toe, dropping something on the foot, or repetitive microtrauma from running in shoes with insufficient toe box clearance. The discoloration is distinguished from melanoma or fungus by its history of trauma, its sharp demarcation, and the fact that it grows out with the nail over months.

Large, painful hematomas can be drained (trephination) by a podiatrist to relieve pressure. If the nail becomes detached or if the discoloration does not move with nail growth, evaluation for other causes is warranted.

3. Psoriatic Nails

Psoriasis affects the nails in 50–80% of patients with skin psoriasis, and nail changes may precede skin involvement. Characteristic findings include pitting (small ice-pick depressions on the nail surface), onycholysis (nail separation), oil-drop discoloration (yellowish-orange spots seen through the nail), subungual hyperkeratosis (buildup of scale under the nail), and nail plate crumbling. Psoriatic nail disease can look remarkably similar to onychomycosis — the two conditions can even coexist. Correct diagnosis drives appropriate systemic or topical treatment for the psoriasis component.

4. Ingrown Toenails (Onychocryptosis)

When the nail edge — most commonly the great toenail — grows into the surrounding soft tissue rather than over it, pain, redness, swelling, and potentially infection result. Ingrown nails develop from improper nail trimming (cutting curved into the corners), shoes with narrow toe boxes, nail trauma, or hereditary nail curvature. Early-stage ingrown nails can be managed with proper trimming, antibiotic soaks, and footwear modification. Moderate and advanced cases are treated by a podiatrist with a simple in-office procedure: removal of the offending nail border with or without chemical matrixectomy (permanent elimination of the nail border to prevent regrowth).

5. Pincer Nail Deformity (Involuted Nail)

Pincer nails are characterized by excessive transverse curvature — the nail curves inward from side to side, constricting the underlying nail bed like a pincer. This can cause significant nail bed pain, particularly with shoe pressure, and may lead to recurrent ingrown nails. Pincer nail deformity may be hereditary, related to osteoarthritis changes in the distal toe joints, or associated with beta-blocker medication use. Treatment ranges from regular professional trimming and packing to surgical nail bed procedures that reshape the underlying nail matrix to flatten the curvature permanently.

6. Onychogryphosis (Ram’s Horn Nail)

Onychogryphosis produces dramatic nail thickening and twisting — the nail takes on a claw or horn shape, sometimes curving sharply in one direction. It occurs most commonly in older adults with reduced mobility and inadequate nail care, but can follow trauma. Regular podiatric nail care is essential for patients with this condition, as the thickened nails cannot be managed with standard nail clippers and can cause significant pressure inside footwear.

7. Melanonychia (Dark Lines or Pigmentation)

Vertical dark streaks (longitudinal melanonychia) or diffuse nail pigmentation can result from multiple causes: melanocyte activation from trauma, medications (hydroxychloroquine, certain chemotherapy agents), Addison’s disease, or most importantly — subungual melanoma. Subungual melanoma is a rare but serious malignancy that can present as a pigmented streak or a dark area under the nail. Features that raise concern include a streak wider than 3mm, irregular borders or color variation, extension of pigment onto surrounding skin (Hutchinson’s sign), nail plate destruction, and occurrence in a single nail of an older individual. Any unexplained dark nail pigmentation warrants evaluation by a dermatologist or podiatrist to rule out melanoma.

8. Nail Trauma and Post-Traumatic Changes

Repetitive microtrauma from running (particularly in shoes with inadequate toe clearance), direct injury, or occupational trauma can cause persistent nail changes: ridging, beau’s lines (horizontal depressions crossing the nail that mark a period of disrupted growth), nail plate splitting, and repeated subungual hematoma formation that eventually leads to permanent nail dystrophy. Addressing the source of the trauma — typically footwear fit — is the primary intervention. Severely damaged nails may be permanently removed to allow the nail bed to toughen if recurring injury is the sole cause of pain.

When to See a Podiatrist About Nail Changes

Seek professional evaluation for nail changes that are painful, involving dark pigmentation (especially vertical streaks), associated with surrounding skin changes or discharge, failing to respond to over-the-counter antifungal treatment after 3 months, or present in someone with diabetes or immune suppression. A podiatrist can examine the nail, culture for fungus, take X-rays if bone involvement is suspected, and biopsy concerning lesions — ensuring the correct diagnosis and appropriate treatment.

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Clinical References

1. Lipner SR, Scher RK. Onychomycosis: clinical overview and diagnosis. Journal of the American Academy of Dermatology. 2019;80(4):835-851.
2. Haneke E. Nail surgery. Clinics in Dermatology. 2013;31(5):516-525.
3. Rich P. Nail disorders: diagnosis and treatment of infectious, inflammatory, and neoplastic nail conditions. Medical Clinics of North America. 2021;105(4):799-813.