Subungual Hematoma vs Fungus: How to Tell the Difference in 30 Seconds

What Is the Real Difference Between a Subungual Hematoma and Nail Fungus?

The core difference is behavior over time, not just color.
A subungual hematoma is trapped blood under the nail caused by trauma. It is locked into the nail plate and moves forward as the nail grows.
Nail fungus (onychomycosis) is an infection. It usually stays in place, spreads backward toward the cuticle, and changes the nail’s texture.

Onycholysis: Why Toenails Lift From the Nail Bed

Quick Self-Check: Bruise or Fungus?

If your spot moves forward after 4 weeks, it’s likely a bruise.
If it stays put, thickens, or creeps backward, think fungus.

Movement beats guessing. Color alone can fool anyone.

Understanding Subungual Hematoma (Bruise Under the Nail)

This YouTube video below by Nabil Ebraheim explains subungual hematoma in detail. He covers causes, symptoms, and treatment options for this common nail injury. These insights highlight the importance of prompt care to prevent complications.

A subungual hematoma forms when trauma breaks tiny blood vessels in the nail bed, allowing blood to collect in the subungual space between the nail plate and nail bed.

Common causes people forget

Tight shoes during long walks or runs (“runner’s toe”)
Dropping something light, not dramatic
Sudden toe impact you barely noticed
Repetitive friction inside the shoe

Many patients say, “I don’t remember hurting it.” That’s very common.

Transverse vs Longitudinal Pigment (This Matters)

Direction tells the story.

Hematoma: transverse (horizontal), blotchy, or irregular
Melanoma: longitudinal melanonychia, a vertical stripe

A bruise is physically trapped in the keratin plate. As the nail matrix pushes out new nail, the distance between the cuticle and the bruise increases month by month. That’s basic nail physics.

Color Timeline of a Bruised Nail (Normal Changes)

Color changes are normal and often cause panic.

Red or maroon → fresh blood
Purple or black → clotted blood
Brown or gray → aging blood
Slight yellow tint → serous residue as it grows out

Color changing does not mean infection by itself.

Does a Bruised Nail Always Hurt?

No.

Fresh hematomas may throb
Older ones are usually painless
Smooth nail surface stays intact

Pain fading does not mean something bad is happening.

Nail Trephination: Draining a Painful Hematoma

Severe pressure sometimes needs nail trephination, a sterile procedure that releases trapped blood.
Never drill, burn, or puncture your nail at home. This can introduce bacteria directly to bone and cause osteomyelitis, a surgical emergency. “Bathroom surgery” is one of the most dangerous nail mistakes.

Understanding Nail Fungus (Onychomycosis)

Onychomycosis is a fungal infection caused by dermatophytes that digest keratin.

Instead of blood, fungus produces subungual hyperkeratosis. This is a chalky, crumbly buildup that lifts the nail (onycholysis) and changes its shape over time.

Signs that point toward fungus

Yellow, white, or cloudy brown color
Thickened nail plate
Rough, brittle, or crumbly surface
Nail lifting with debris underneath
Usually little or no pain

Fungus does not travel forward cleanly like a bruise.

The Texture Test (Very Useful at Home)

Gently run a clean fingernail across the surface.

Smooth and glassy: pigment is under the nail (bruise or melanoma)
Pitted or chalky: fungal breakdown of the nail plate

Texture often tells more than color.

What About Thin Vertical Lines? (Splinter Hemorrhages)

Not every line is cancer.

Splinter hemorrhages are tiny, thin red-brown lines caused by small capillary bleeds.

Usually multiple
Very thin
Move forward with nail growth
Often caused by friction or minor trauma

They are not melanoma. Melanoma stripes are wider, darker, and don’t move.

Subungual Hematoma vs Fungus: Side-by-Side Comparison

Feature	Subungual Hematoma (Bruise)	Nail Fungus (Onychomycosis)
Cause	Trauma	Fungal pathogen
Pigment direction	Transverse / blotchy	Irregular or spreading
Movement	Moves forward with growth	Stays or spreads backward
Nail thickness	Normal	Thickened
Nail bed surface	Smooth	Chalky debris
Pain	Early pressure	Usually painless

This table alone answers most questions fast.

The Critical Red Flag: Subungual Melanoma

Rare, but serious. This must be addressed clearly.

Warning signs

Dark band that does not move
Vertical stripe (longitudinal melanonychia)
Pigment spreading onto surrounding skin
Nail splitting or destruction without trauma

This is not something to monitor casually.

🚨 Hutchinson’s Sign (Safety Box)

Hutchinson’s sign means pigment has spread into the periungual skin (cuticle or nail folds).

Key distinction:

A bruise is strictly subungual
It will never leak into the skin

If pigment looks like ink bleeding into paper, seek care promptly.

What the Doctor Looks For (Why Exams Matter)

Dermatologists often use dermoscopy, a magnified light tool.

Bruise: granular color clumps
Melanoma: pigment networks or irregular lines

This is why professionals can tell things apart when photos alone can’t.

One More Pro Tip: The Acetone Test

Sometimes dark spots aren’t medical at all.

Hair dye
Sock dye
Chemical stains

Try this once:

Dip a Q-tip in acetone
Gently rub the nail surface

If color comes off, it’s just surface staining.

Multiple Nails Turning Dark? Think Systemic

If several nails change color at the same time without trauma, consider:

Certain medications (chemotherapy, antimalarials)
Hormonal or endocrine conditions
Addison’s disease

This pattern is rarely a bruise or fungus.

Does a Bruised Toenail Always Fall Off?

No.
Nails usually shed only when a hematoma covers 25–50% or more of the nail bed. Smaller bruises often grow out normally.

Can I Use Antifungal Cream on a Bruise?

This YouTube video below by The London Podiatrist demonstrates how to properly apply antifungal cream. It covers techniques, frequency, and tips for effective treatment. These insights highlight the importance of correct application for faster nail recovery.

It won’t hurt, but it won’t help.
Antifungals cannot penetrate a blood pocket.

Recovery Window (Set Expectations)

Toenails grow about 1 mm per month.

Small hematoma: 3–4 months
Large hematoma: 6–9 months to fully trim away

Checking weekly only increases anxiety. Monthly checks make more sense.

When Should You See a Doctor?

Get evaluated if:

The spot doesn’t move after 4–6 weeks
The nail thickens or crumbles
Pigment spreads onto skin
A vertical dark stripe appears
Several nails change together

Guidelines often follow standards from the American Academy of Dermatology (AAD).

Final Thought

A dark spot under a nail is scary, and that fear is valid.
But most cases are either a bruise that grows out or a fungus that slowly changes texture.

Watch movement. Feel texture. Respect red flags. Your nail is giving you clues. When you know how to read them, panic turns into clarity.