Brown Toenail: 7 Causes & How a Podiatrist Can Help

You glance down at your feet and notice one of your toenails has turned an odd shade of brown. Maybe it happened gradually; maybe it seemed to appear overnight. Either way, your first question is probably the same: Is this serious?

The honest answer: it depends. A brown toenail can be completely harmless — a faded remnant of old nail polish — or it can be an early sign of a fungal infection, a systemic health condition, or in rare cases, something that needs urgent attention.

This guide walks you through the 7 most common causes of brown toenail discoloration, how to tell them apart, and exactly when it’s time to stop guessing and see a podiatrist.

7 Common Causes of Brown Toenails

Toenail discoloration rarely has just one cause — but these seven account for the vast majority of cases podiatrists see in clinical practice.

1. Toenail Fungus (Onychomycosis)

Toenail fungus is the single most common cause of brown, yellow, or thickened nails. The fungal infection (onychomycosis) invades the nail bed and causes the nail to discolor, thicken, and become brittle over time.

What it looks like: Starts as a white or yellow spot under the nail tip. As it spreads, the nail turns brown, yellow, or greenish, and may separate from the nail bed (onycholysis). The nail often becomes thick and chalky.

Who’s most at risk: Swimmers, gym-goers, people with diabetes, and anyone who wears tight or sweaty shoes regularly.

Fungal infections do not resolve on their own. Over-the-counter antifungal nail polish has limited effectiveness for established infections. A podiatrist can prescribe oral antifungals, prescribe topical medications, or recommend laser therapy — which offers higher cure rates than topical treatments alone.

2. Trauma / Subungual Hematoma

Dropping something on your toe, stubbing it hard, or repetitive pressure from running or ill-fitting shoes can cause bleeding under the nail. This trapped blood (a subungual hematoma) appears dark brown, maroon, or black.

How to tell: There’s usually a clear injury event you can trace it back to. The nail may be painful to press on shortly after the injury. Over several months, the discoloration will grow out with the nail.

3. Psoriasis

Nail psoriasis affects up to 50% of people with skin psoriasis and can cause significant toenail changes, including brown or yellow-brown discoloration (called an “oil spot” or “salmon patch” underneath the nail), pitting, and nail thickening.

What makes it different: Psoriatic nail changes typically affect multiple nails at once and may come alongside skin psoriasis symptoms elsewhere on the body. The nail may look oily or have a distinctive yellow-brown patch near the tip.

4. Subungual Melanoma (When to Worry)

Subungual melanoma is a rare but serious form of skin cancer that develops under the nail. It can appear as a brown or black streak (called melanonychia) running lengthwise down the nail.

Warning signs that require urgent evaluation: A dark streak that is getting wider over time, a streak that spans more than 1/3 of the nail width, spread of pigment onto the surrounding skin (called Hutchinson’s sign), or a new streak with no history of nail trauma.

Subungual melanoma is disproportionately common in people with darker skin tones and is frequently misdiagnosed as a fungal infection. If there’s any doubt, see a dermatologist or podiatrist promptly — early diagnosis dramatically improves outcomes.

5. Shoe Friction & Pressure

Tight shoes, pointed toe boxes, or footwear that causes the toes to jam forward repeatedly are a very common (and entirely benign) cause of brown toenail discoloration — especially in runners and hikers.

Solution: Switch to well-fitted shoes with a wider toe box. Trim nails straight across. If the nail is lifting away from the bed due to chronic friction, a podiatrist can assess whether intervention is needed.

6. Nail Polish Staining

Dark-pigmented nail polishes — especially deep reds, plums, and browns — can leach pigment into the nail plate over time, leaving a yellowish or brownish stain even after removal.

How to tell: Staining tends to be superficial (on the surface of the nail), uniform in color, and fades with time or gentle buffing. It appears on the nails you painted, not underneath the nail.

Prevention: Always apply a clear base coat before using pigmented polish, and avoid leaving polish on for more than 2 weeks at a stretch.

7. Systemic Health Conditions

Several internal health conditions can manifest through changes in the nails. Brown or discolored toenails may signal:

• Diabetes — poor circulation and immune function make diabetics highly prone to nail infections and color changes
• Kidney disease — a condition called “half-and-half nails” (Lindsay’s nails) causes the lower half of the nail to appear brown
• Liver disease — nails may turn brown or white (Terry’s nails)
• Thyroid disorders — can cause nail thickening, brittleness, and discoloration
• Nutritional deficiencies — particularly B12, zinc, or iron deficiencies

If you have a chronic health condition and notice new nail changes, mention them to your doctor or podiatrist at your next visit. Nails are sometimes the first visible indicator of systemic changes.

Brown vs. Black vs. Yellow Toenails — What’s the Difference?

Not all toenail discoloration is the same. Here’s a quick reference guide to help you interpret what you’re seeing:

Remember: this table is a general guide, not a diagnostic tool. Multiple colors can appear in the same nail, and some causes — particularly melanoma — can mimic benign conditions. When in doubt, get it checked.

How a Podiatrist Diagnoses Toenail Discoloration

A podiatrist doesn’t just look at your nail and guess. A proper nail evaluation typically involves:

• Visual and physical examination of all nails, not just the affected one
• Patient history — duration of discoloration, any injury, shoe type, sports activity, existing health conditions
• Nail clipping or scraping for laboratory fungal culture (if infection is suspected)
• Dermoscopy — a magnified examination tool that helps distinguish melanonychia from benign pigmentation
• In some cases, referral to a dermatologist for nail biopsy if melanoma cannot be ruled out

Getting the correct diagnosis matters because the treatment for fungal nails is completely different from the treatment for traumatic nails or psoriatic nails. Treating the wrong condition wastes time and money — and in the case of melanoma, delays critical care.

Treatment Options by Cause

Once your podiatrist has a confirmed diagnosis, treatment is tailored to the specific cause:

Home Remedies: What Works and What Doesn’t

What Actually Helps

• Tea tree oil (diluted) — has mild antifungal properties; best for very early, superficial fungal changes
• Keeping nails clean, trimmed straight across, and dry — reduces fungal spread and friction
• Switching to breathable, well-fitted footwear — prevents trauma-related and friction-related discoloration
• Wearing moisture-wicking socks — keeps the nail environment hostile to fungal growth
• Using a clear base coat under nail polish — prevents cosmetic staining

What Doesn’t Work (Despite What the Internet Says)

• Undiluted bleach or hydrogen peroxide — can damage skin and nail tissue; not effective for true nail fungus
• Apple cider vinegar soaks — no clinical evidence supports this as a standalone treatment for onychomycosis
• Over-the-counter antifungal nail polish alone — effective only for superficial nail infections, not for established infections that have penetrated the nail plate
• Waiting and hoping it goes away — fungal infections and melanoma do not resolve without treatment

When Should You See a Podiatrist?

You should make an appointment if any of the following apply:

• The brown discoloration has lasted more than 2 months
• The nail is thickening, crumbling, or separating from the nail bed
• There is pain or tenderness around the nail
• The discoloration is spreading to other nails
• A dark streak is running lengthwise down the nail with no known injury
• You have diabetes, peripheral vascular disease, or a weakened immune system
• You’re not sure of the cause

The Bottom Line

A brown toenail is your body’s way of flagging something that deserves attention — even if it turns out to be nothing serious. The problem is that the causes range from completely benign (nail polish stain) to conditions that genuinely need medical care (fungal infection, melanoma, systemic disease).

The only way to know for certain is to have it evaluated by a professional. A podiatrist can diagnose the cause accurately, rule out anything serious, and give you a clear treatment plan — all in a single appointment.

Don’t let uncertainty sit for months. A same-week nail care evaluation takes less time than you’d expect, and the peace of mind is worth it.