Toenail changes can develop gradually and may go unnoticed at first. A nail may become yellow, thick, brittle, or unusually shaped. Some patients also notice that the nail begins to crumble or separate from the skin underneath.
One common cause of these changes is onychomycosis, a fungal infection that affects the toenails. Although it may begin as a small cosmetic concern, the infection can spread, cause discomfort, and make nail care more difficult.
At Orange County Foot & Ankle Institute, Dr. Amir Lebaschi, DPM evaluates fungal toenail infections to identify the underlying cause and recommend appropriate treatment options.
What Is Onychomycosis?
Onychomycosis is a fungal infection involving the nail plate, nail bed, or surrounding nail structures.
The infection often begins near the tip or side of the toenail. As it progresses, the nail may become thicker, discolored, brittle, or separated from the nail bed.
Fungi can grow in warm, moist environments, making the feet particularly vulnerable when shoes and socks trap moisture.
Toenail fungus commonly affects the big toenail, although several nails may become infected.
Without treatment, the infection may persist and gradually involve more of the nail.
What Causes Fungal Toenail Infections?
Onychomycosis develops when certain fungi infect the nail.
Dermatophytes are the most common cause, although some yeast and molds can also produce nail infections.
Several factors may increase the risk of developing onychomycosis.
Common risk factors include:
- Excessive foot sweating
- Wearing damp socks or shoes
- Walking barefoot in public showers or locker rooms
- Previous athlete’s foot infections
- Repeated toenail injuries
- Tight or poorly fitting footwear
- Older age
- Diabetes
- Poor circulation
- A weakened immune system
- Sharing contaminated nail-care tools
Fungal organisms can enter through small breaks in the skin or areas where the nail has become damaged.
How Fungal Infections Change Toenail Appearance
Fungal infections can affect both the appearance and structure of the toenail.
As the infection progresses, the nail may develop several noticeable changes.
1. Yellow or White Discoloration
One of the earliest signs of onychomycosis is a change in nail color.
The toenail may develop white, yellow, or yellow-brown patches. Discoloration often begins near the tip or side of the nail before spreading.
However, nail discoloration does not always indicate fungus. Trauma, psoriasis, and other conditions may cause similar changes.
2. Thickened Toenails
Fungal infections can cause the toenail to become abnormally thick.
As the nail changes, it may become harder to trim and more uncomfortable inside shoes.
Thickened nails can also create pressure against the surrounding skin, especially during walking or exercise.
3. Brittle or Crumbling Nails
An infected toenail may become fragile and break easily.
The nail edges may crumble, split, or appear uneven. In advanced cases, portions of the nail may become significantly damaged.
These changes can make everyday nail care more difficult.
4. Debris Under the Toenail
Fungal infections can lead to a buildup of thickened material beneath the nail.
This debris may appear white, yellow, or crumbly. As material accumulates, it can cause the nail to lift away from the nail bed.
5. Toenail Separation
Onycholysis occurs when the nail plate separates from the underlying nail bed.
A fungal infection is one possible cause.
Patients may notice a white or yellow gap beneath the nail. The loose nail may also catch on socks or shoes.
Once the nail separates, the detached portion generally cannot reattach. Healthy nail growth must gradually replace it.
6. Changes in Nail Shape
As onychomycosis progresses, the toenail may become distorted or irregular.
The nail may develop ridges, uneven thickness, or abnormal curvature.
Severe changes can make wearing shoes uncomfortable and may increase pressure around the toes.
Can Toenail Fungus Spread?
Yes. Fungal toenail infections can spread to other nails and surrounding skin.
The infection may also occur alongside athlete’s foot, a fungal skin condition that affects the feet.
Fungi can spread through contaminated surfaces, damp environments, shared nail tools, and footwear.
Proper foot hygiene and early treatment can help reduce the risk of transmission and recurrence.
Why Onychomycosis Should Not Be Ignored
Toenail fungus is not always an urgent medical problem, but it can become uncomfortable and difficult to manage.
As the nail thickens, it may create pressure inside shoes. Brittle or loose nail edges may also irritate the surrounding skin.
For patients with diabetes, neuropathy, or poor circulation, thickened or damaged nails deserve particular attention.
Nerve damage may reduce the ability to feel pressure or injury. Poor circulation can also complicate healing if the surrounding skin becomes damaged.
These patients should avoid aggressively trimming or removing thickened nails at home
How Is Onychomycosis Diagnosed?
Not every thick, yellow, or damaged toenail has a fungal infection.
Toenail trauma, psoriasis, eczema, and other nail disorders can produce similar symptoms.
A proper diagnosis helps prevent unnecessary treatment and identifies the actual cause of nail changes.
During an evaluation, Dr. Amir Lebaschi, DPM may assess:
- Nail color and thickness
- Changes in nail shape
- Brittle or crumbling nail edges
- Debris beneath the nail
- Toenail separation
- Surrounding skin changes
- Previous nail injuries
- Footwear-related pressure
- Diabetes or circulation concerns
When appropriate, a nail clipping or sample of material beneath the nail may be collected for laboratory testing.
Testing can help confirm fungal infection before prescription treatment begins.
Treatment Options for Onychomycosis
Fungal toenail treatment depends on the severity of the infection, the number of nails affected, and the patient’s medical history.
Treatment may include topical medications, oral antifungal therapy, professional nail care, or a combination of approaches.
Topical Antifungal Medication
Prescription topical antifungal treatments may be appropriate for mild or limited nail infections.
These medications are applied directly to the affected nail.
Treatment usually requires consistent application over several months. Topical medications may be less effective when the nail is very thick or when the infection affects a large portion of the nail.
Oral Antifungal Medication
Oral antifungal medication may be recommended for more extensive or persistent infections.
Terbinafine is a commonly prescribed oral treatment for dermatophyte toenail infections.
Oral antifungal medications generally have higher cure rates than topical treatments, but they are not appropriate for everyone.
A healthcare provider should review liver health, current medications, and possible drug interactions before prescribing treatment.
Professional Nail Trimming and Debridement
A podiatrist may carefully trim or reduce thickened nail tissue.
This can help relieve pressure, improve comfort, and make nail care easier.
Professional nail reduction may also improve the effectiveness of certain antifungal treatments when used alongside medication.
However, trimming or thinning the nail alone does not reliably eliminate the fungal infection.
Nail Removal in Selected Cases
In certain situations, a severely thickened, painful, or damaged toenail may require partial or complete removal.
This is not a routine treatment for every fungal nail infection.
A podiatrist can determine whether nail removal is appropriate based on the severity of the condition and the patient’s overall foot health.
Does Laser Treatment Work for Toenail Fungus?
Some clinics offer laser-based procedures for fungal toenails.
However, evidence supporting laser treatment as a reliable cure remains limited.
Certain devices have received FDA clearance for temporary improvement in the appearance of affected nails, which is different from proving that they consistently eliminate fungal infection.
Patients should understand the available evidence, possible costs, and treatment limitations before considering laser procedures.
Prescription antifungal medications remain the more established treatment options for confirmed onychomycosis.
How Long Does It Take for a Fungal Toenail to Improve?
Toenail fungus treatment requires patience because toenails grow slowly.
Even after successful antifungal treatment, the damaged portion of the nail may remain visible until healthy new nail grows forward.
A big toenail may take approximately 12 to 18 months to grow out completely.
Some patients may notice healthy nail growth near the base of the nail before the entire nail appears normal.
If the nail has sustained permanent damage, it may not return completely to its previous appearance.
Treatment results vary depending on the severity of the infection, medication effectiveness, nail growth, and underlying health conditions.
Can Toenail Fungus Return After Treatment?
Yes. Onychomycosis can return even after successful treatment.
Fungi may remain on the surrounding skin, inside footwear, or in damp environments.
Patients with recurring athlete’s foot, excessive sweating, nail trauma, or certain medical conditions may have a higher risk of reinfection.
Preventive foot care can help reduce the likelihood of recurrence.
How to Help Prevent Fungal Toenail Infections
Several daily habits can help protect the toenails
Helpful steps include:
- Washing and drying the feet regularly
- Drying carefully between the toes
- Changing socks daily
- Avoiding prolonged use of damp footwear
- Wearing breathable shoes
- Using protective footwear in public showers and locker rooms
- Trimming toenails carefully
- Avoiding shared nail clippers
- Cleaning nail-care tools after use
- Treating athlete’s foot promptly
- Avoiding repeated toenail pressure and trauma
- Monitoring nail changes regularly
Patients with diabetes should inspect their feet and toenails daily for changes.
When Should You See a Podiatrist?
Schedule a podiatric evaluation if you notice:
- Yellow, white, or brown toenail discoloration
- Toenails becoming unusually thick
- Brittle or crumbling nail edges
- Debris collecting beneath the nail
- A toenail separating from the nail bed
- Changes in nail shape
- Pain when wearing shoes
- Recurring fungal nail infections
- Multiple affected toenails
- Nail problems associated with diabetes or poor circulation
Seek prompt medical attention if the surrounding skin becomes increasingly red, swollen, painful, or begins draining pus.
A new or changing dark streak beneath the nail should also be evaluated, especially if the discoloration extends onto surrounding skin.
The Bottom Line
Onychomycosis is a fungal infection that can gradually change the appearance, thickness, and structure of toenails.
Common signs include yellow or white discoloration, nail thickening, crumbling edges, debris beneath the nail, and separation from the nail bed.
Although some fungal nail infections cause little discomfort, more advanced cases may create pressure, pain, and difficulty with nail care.
Accurate diagnosis is important because several other nail conditions can look similar to fungal infections.
At Orange County Foot & Ankle Institute, Dr. Amir Lebaschi, DPM evaluates fungal toenails, thickened nails, nail discoloration, and other toenail abnormalities to determine appropriate treatment options.
If your toenails are becoming thick, discolored, brittle, or loose, a podiatric evaluation can help identify the cause and guide the right treatment plan.
Medical References
- American Academy of Dermatology – Nail Fungus Diagnosis and Treatment:
https://www.aad.org/public/diseases/a-z/nail-fungus-treatment - American Family Physician – Diagnosis and Management of Tinea Infections (2025):
https://www.aafp.org/afp/2025/1000/tinea-infections - British Association of Dermatologists – Fungal Nail Infection Guideline (2026):
https://doi.org/10.1093/bjd/ljag318