Thick toenails are one of the most common foot complaints I see in clinic. But “thick toenails” isn’t a diagnosis — it’s a symptom with 7 different possible causes, each with a different treatment. Dr. Tom Biernacki DPM explains how to tell them apart.

7 Causes of Thick Toenails

1. Onychomycosis (Toenail Fungus) — Most Common Cause

Fungal infection is responsible for 50% of all thick toenail cases. Signs: yellow/brown discoloration, brittle or crumbling edges, white chalky buildup under the nail, foul odor. Spreads to adjacent nails if untreated. Requires antifungal treatment — does NOT resolve on its own.

2. Onychogryphosis (Ram’s Horn Nail)

A curved, thickened nail that grows in a claw-like shape. Most common in elderly patients who have neglected nail care. Caused by repeated trauma, poor circulation, or chronic pressure from ill-fitting shoes. Requires professional debridement and regular podiatric nail care.

3. Psoriasis

Nail psoriasis causes thickening, pitting (tiny holes), oil spots (yellowish-brown patches), and separation of the nail from the nail bed (onycholysis). Often affects multiple nails simultaneously and frequently accompanies skin psoriasis plaques elsewhere on the body.

Watch: Dr. Biernacki Explains Thick Toenails

Dr. Tom Biernacki, DPM | Balance Foot & Ankle — Howell & Bloomfield Township, MI | (810) 206-1402

4. Trauma (Subungual Hematoma / Repeated Microtrauma)

Shoes that are too short cause the nail to repeatedly hit the toe box during walking and running. Over time, this causes the nail to thicken as a defensive response. Black or brown discoloration may be present from accumulated blood under the nail.

5. Aging (Nail Dystrophy)

After age 60, nails naturally grow more slowly and can thicken as they lose moisture. The nail matrix (the growth center) becomes less efficient. This is a benign condition, but it does make nails harder to trim and more prone to ingrowth.

6. Poor Circulation / Peripheral Artery Disease

Reduced blood flow to the feet affects nail health. Thickened, slow-growing nails with surrounding dry skin, loss of foot hair, and cold feet may indicate peripheral arterial disease (PAD). This requires medical evaluation — not just nail treatment.

7. Yellow Nail Syndrome

A rare condition associated with lymphedema, respiratory conditions, or rheumatoid arthritis. All nails turn yellow and thicken simultaneously, often with slow growth and onycholysis.

How to Tell Fungus from Non-Fungus

The only definitive way is a nail culture or PCR test ordered by your podiatrist. However, fungus is most likely if: the nail is yellowed or brownish, crumbles at the edges, has white powder under it, smells unpleasant, or only one or two nails are affected (rather than all ten equally).

Treatment by Cause

• Fungal: Prescription topical antifungal (efinaconazole), oral antifungal, or laser treatment
• Onychogryphosis: Professional trimming and debridement every 6-8 weeks
• Psoriasis: Coordination with dermatology ± topical steroids to nail bed
• Trauma: Properly fitted shoes (thumb-width of space at the toe), possibly nail avulsion
• Aging/Poor circulation: Regular podiatric nail care, vascular evaluation if suspected PAD

Thick toenails that are painful, discolored, or affecting multiple nails deserve a professional evaluation — especially if you’re diabetic or have circulation issues. Don’t let them go untreated.

Balance Foot & Ankle — (810) 206-1402 | Howell & Bloomfield Hills, MI

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.