What Causes Toenails to Thicken? Causes, Treatment, and Prevention

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

Why Toenails Thicken: Understanding the Causes

Toenail thickening — onychauxis — is one of the most common nail complaints podiatrists evaluate. While the appearance is similar across different causes, the underlying mechanism and appropriate treatment vary significantly. Correctly identifying why a toenail has thickened directs treatment and prevents ineffective self-management. At Balance Foot & Ankle in Howell and Bloomfield Township, Michigan, we evaluate thickened toenails systematically to identify the specific cause before recommending treatment.

Onychomycosis: Fungal Nail Infection

Fungal nail infection is the most common cause of toenail thickening, affecting approximately 10% of the general population and up to 50% of adults over 70. The dermatophyte fungi (most commonly Trichophyton rubrum) invade the nail plate, producing enzymes that degrade keratin and cause the nail to thicken, discolor (yellow-brown), become brittle, and separate from the nail bed (onycholysis). Diagnosis should be confirmed with nail clippings sent for PAS staining or fungal culture before initiating systemic antifungal treatment — clinical appearance alone has a false-positive rate of 50% for fungal infection.

Traumatic Onychauxis

Repeated microtrauma — from shoes that are too short causing the nail to repeatedly impact the toe box, from athletic activity, or from occupational footwear — causes the nail matrix to produce thicker nail plate as a protective response. The nail thickens uniformly without the discoloration or brittleness typical of fungal infection. Addressing footwear fit resolves the underlying cause; nail reduction (debridement) manages symptoms while the cause is addressed.

Psoriasis and Nail Involvement

Psoriasis affects nails in 80% of patients with skin psoriasis and in some patients as the only site of involvement. Nail psoriasis causes thickening, pitting (pinpoint depressions in the nail surface), onycholysis, and subungual hyperkeratosis (buildup under the nail). It can be impossible to distinguish from onychomycosis clinically — nail cultures help differentiate, though both conditions can coexist.

Age-Related Nail Changes

Normal aging produces slower-growing, thicker, more brittle nails — particularly in the great toenails. Age-related thickening (physiologic onychauxis) is not associated with discoloration, brittleness, or nail bed separation characteristic of fungal infection. Regular professional nail debridement prevents the pressure and discomfort that can result from excessively thickened nails, particularly important in older patients who cannot safely trim their own nails. Contact Balance Foot & Ankle at (810) 206-1402 for evaluation and treatment of thickened toenails.

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When to See a Podiatrist for Thick Toenails

Thickened toenails can result from fungal infection, trauma, circulation problems, or skin conditions like psoriasis. At Balance Foot & Ankle, Dr. Tom Biernacki identifies the cause of nail thickening and provides professional nail care, antifungal treatment, and guidance for managing thick nails long-term.

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Clinical References

1. Gupta AK, Versteeg SG, Shear NH. Onychomycosis in the 21st century: an update on diagnosis, epidemiology, and treatment. J Cutan Med Surg. 2017;21(6):525-539.
2. Baran R, Dawber RP, Haneke E, et al. A text atlas of nail disorders: techniques in investigation and diagnosis. 3rd ed. London: Martin Dunitz; 2003.
3. De Berker D. Clinical practice: fungal nail disease. N Engl J Med. 2009;360(20):2108-2116.

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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.