Toenail Color Changes Explained: What Each Nail Color Signals About Your Health

Toenail Color Changes and What Each Color Signals

Most people notice toenail problems with their eyes first. A strange color. A dark line. A green patch that wasn’t there before. And the first question is always the same. What does this color actually mean?

Toenail color changes are not random. In medical terms, they are called chromonychia, and they often reflect what’s happening under the nail plate. Sometimes it’s fungus. Sometimes it’s trauma. And sometimes, it’s a signal that has nothing to do with the nail itself. This guide works like a color map. You match what you see to what it usually means. Then you decide how urgent it is.

Toenail Color Changes and What Each Color Signals

What Do Toenail Color Changes Mean?

Toenail color changes can signal infections, injuries, or systemic health issues. Yellow or cloudy nails most often indicate onychomycosis (fungal infection). Black or purple discoloration usually comes from a bruise (subungual hematoma), but dark streaks that don’t move may indicate subungual melanoma. Green nails are commonly caused by Pseudomonas aeruginosa, a bacterial infection. White, blue, or red changes may reflect trauma, circulation problems, or internal disease. The color, pattern, and movement over time determine urgency. Color is information. Pattern is context.

Toenail Color Chart: Quick Diagnostic Overview

Nail Color	Most Common Cause	Urgency Level
Yellow / Cloudy	Fungal infection (Onychomycosis)	Routine
White spots	Minor trauma or surface fungus	Low
Black / Brown	Bruise, melanoma, or dark fungus	Moderate–High
Green	Bacterial infection (Pseudomonas)	Moderate
Blue	Oxygen or medication related	High
Red streaks	Trauma or vascular issue	Moderate

As a rule, if a color change covers more than 25% of the nail, it deserves professional attention.

Yellow or Cloudy Nails: The Classic Fungal Signal

Yellow or cloudy nails often signal fungal infection, but color alone never tells the full story. Understanding why onychomycosis develops even with good hygiene helps explain persistent discoloration, nail thickening, and repeated treatment failure. When yellowing worsens despite care, deeper causes deserve attention.

What’s happening biologically

In onychomycosis, fungi break down keratin, the protein that makes up the nail. This process, called keratinolysis, causes the nail to look opaque, matte, and friable (crumbly), especially at the distal edge.

What different yellow shades mean

Dull or pale yellow: early fungal activity
Deep yellow or orange-brown: higher fungal load and thicker nail

As fungus progresses, the nail often lifts from the bed. This is called onycholysis, and it allows color, moisture, and debris to get trapped underneath.

Important differential: Yellow Nail Syndrome

If every nail is thick, deep yellow, and barely growing, fungus may not be the cause. Yellow Nail Syndrome (YNS) is a rare systemic condition linked to lymphatic or respiratory issues. A key clue is growth rate. Growth test: if you haven’t needed to trim the nail in three months and the cuticle appears absent, think systemic rather than fungal.

Black or Dark Brown Nails: Bruise, Fungus, or Melanoma?

Dark nails create the most anxiety. And for good reason.

Subungual Hematoma (Bruise)

This happens when blood becomes trapped under the nail after trauma.

Typical signs

Pain followed an injury
Color appears purple, maroon, or red-black
The discoloration moves forward as the nail grows

Because toenails grow about 1.5–2mm per month, you should see a clear band of pink nail at the base within 8–10 weeks. If the dark area stays fixed after three months, it’s not a bruise and needs evaluation.

Black Onychomycosis (Rare but Real)

Some dematiaceous (dark-pigmented) fungi can cause black or brown onychomycosis. These nails are usually opaque and friable, not smooth like a bruise. This condition can mimic melanoma, which is why confirmation matters.

What Is Hutchinson’s Sign?

Hutchinson’s Sign occurs when dark pigment from a nail streak extends onto the eponychium (cuticle) or surrounding skin. In clinical practice, this is considered subungual melanoma until proven otherwise. It requires urgent dermatologic evaluation. This is not a watch-and-wait situation.

Green Nails: Green Nail Syndrome (Pseudomonas)

This YouTube video below by Doctorpedia explains green nail syndrome and its common causes. It outlines daily care tips and treatment guidance. These insights stress proper hygiene to restore healthy nails.

A green toenail is almost always bacterial.

What does a green toenail mean?

Green Nail Syndrome is caused by Pseudomonas aeruginosa, a bacterium that thrives in moist environments, especially under a lifted nail.

The green color comes from Pyocyanin and Pyoverdine, pigments secreted by the bacteria. These pigments stain the nail plate and may persist until the nail grows out.

Crucial step:
Do not seal a green nail with clear polish or antifungal lacquer. Trapping the nail creates an anaerobic environment that allows Pseudomonas to thrive and deepen its colonization.

White Nails: Trauma, Fungus, or Systemic Clue

White discoloration has several meanings.

Punctate Leukonychia

Small, isolated white dots. These are tiny injuries to the nail matrix. Harmless. They grow out.

White Superficial Onychomycosis

Chalky white patches on the surface that scrape easily. This is a superficial fungal infection.

Terry’s Nails

The entire nail looks white or “ground glass,” with a thin pink band at the tip. This can be associated with liver, kidney, or circulatory disorders. If the whole nail turns white, don’t assume fungus.

Blue or Red Nails: Systemic Signals

Blue Nails (Cyanosis)

A blue or dusky tint can indicate low oxygen levels or medication effects. This is not a nail problem. It’s a systemic signal and needs medical review.

Red Lines and Splinter Hemorrhages

Splinter hemorrhages are thin red or brown lines that are always longitudinal, running the length of the nail. They look like tiny wood splinters.

One nail after trauma is common
Multiple streaks across several nails may signal infective endocarditis or vascular disease

This should be mentioned to a physician.

Exogenous vs Endogenous Pigmentation

Not all discoloration is medical.

Exogenous pigmentation: stains from socks, polish, chemicals
Endogenous pigmentation: blood, bacteria, fungus, or disease

At-home test:
Use a cotton swab with a small amount of acetone.

Color transfers → exogenous
Color stays → endogenous and needs evaluation

True medical color doesn’t wipe off.

The “Check the Cuticle” Rule

If discoloration:

Starts near the cuticle
Extends into surrounding skin
Does not move with growth

Urgency increases. Always check the cuticle.

Why Colors Get Trapped Under the Nail

Once the nail lifts, discoloration becomes harder to clear because organisms settle beneath the plate. This process, known as onycholysis, creates the ideal environment for fungus, bacteria, or trapped blood to persist until the nail grows out or receives targeted treatment.

Fungus (yellow or brown)
Bacteria (green)
Blood (black or purple)

Correcting the lift is often key to correcting the color.

When to See a Doctor Immediately

Don’t delay if you notice:

Dark vertical streaks on a single nail
Pigment spreading into the cuticle
Green discoloration with nail lifting
Rapid color change with pain or swelling

Early evaluation protects the nail matrix and, in rare cases, your life.

Final Thoughts

Yellow usually means fungus
Green means bacteria
Black can be trauma or something serious
White, blue, or red often point beyond the nail

Toenail color isn’t cosmetic trivia. It’s a health signal.

Look at the color. Check the cuticle. Watch for movement. Your toenails talk quietly. Learning to listen early makes all the difference.