Black Spot on Nail Causes, Treatment and Diagnosis

Black Spot on Fingernail

A black mark on the fingernail may be due to various reasons. Some of the most common causes of black spot on nail include:

Trauma or Injury:

• A tiny bruise or blood blister below the nail (subungual hematoma) might manifest as a dark or black spot. It occurs usually after a blow to or bumps on the finger.

Fungal Infection:

• Fungal infections may result in color changes or darkening of the nail.

Melanonychia:

• This is a situation in which a pigmented band or spot on the nail results from excessive melanin formation. It may be benign but at other times needs medical assessment.

Melanoma (Nail Cancer):

• A darkening spot or streak that enlarges, changes in shape, or spreads might be an indication of melanoma beneath the nail, a condition that is severe and requires immediate medical intervention.

Other Causes:

• Nail psoriasis
• Some medications or chemicals
• Systemic diseases (rare)

Black Line on Nail

A black line on the nail may signify various things based on its description. Here are some of the possible common ones:

Common Reasons for a Black Line on a Nail

Melanonychia

• A disease in which there is a longitudinally (cuticle to tip) dark brown or black line on the nail. It's due to hyperpigmentation within the nail matrix. It may be benign or occasionally an alarm sign.

Splinter Hemorrhages

• Black or reddish, thin lines underneath the nail that resemble splinters. They may appear as a result of small blood clots under the nail due to trauma or some medical conditions such as infections or vasculitis.

Trauma

• Damage to the nail leads to bleeding under the nail, which is seen as a dark line or streak.

Subungual Melanoma

• A rare but significant cause, this is a form of skin cancer that begins under the nail. Warning signs are a broadening dark line, changes in shape or color, or paired with nail deformity or bleeding.

Medications or Chemicals

• Certain medications or exposure to chemicals may result in pigment alteration in nails.

Black Spot under Toenail

A black spot below the toenail is most commonly due to:

Frequent Causes of Black Spot below Toenail

Subungual Hematoma (Blood Bruise):

• This occurs when you knock your toe—such as stubbing your toe or wearing tight shoes—and blood accumulates beneath the nail, resulting in a black or dark red spot.

Fungal Infection:

• Certain fungal infections may result in discoloration or dark spots under the nail.

Melanonychia:

• A pigmented band or spot beneath the nail due to hyperpigmentation of melanin.

Subungual Melanoma:

• A rare but dangerous cause. If the black spot increases, extends, or alters shape, or with pain or nail deformity, it must see a doctor at once.

Nail Melanoma Symptoms

Nail melanoma (subungual melanoma) is a very rare but dangerous type of skin cancer that occurs beneath the nail. It's easy to misdiagnose, so early detection is important. 

Common Symptoms of Nail Melanoma:

Dark Stripe (Longitudinal Melanonychia):

• Brown, dark grey or black vertical stripe from the cuticle to the end of the nail.
• Usually occurs on a single nail (usually thumb or big toe).

Stripe Changes:

• Stripe widens or darkens with time.
• The edges can become irregular or soft.

Pigment Spread:

• The pigment spreads to the skin around the cuticle or nail fold (Hutchinson's sign).

Nail Changes:

• The nail becomes brittle, cracked, or raised.
• Deformity or loss of the nail.

No Trauma History:

• Tends to appear without a known injury.

Pain or Bleeding:

• Later, there can be pain, oozing, or bleeding from the nail bed.

Subungual Hematoma Treatment

A subungual hematoma is when blood accumulates under the nail from trauma—such as stubbing your toe or something falling on your finger.

When It's Mild (Small, painless spot):

• When the hematoma is painless, small, and does not alter the shape of the nail or cause pain:
• No treatment is required.
• Keep it clean. The blood will gradually grow out with the nail over weeks to months.
• Avoid pressure or tight footwear.
• Watch for any change (in size, color, or pain).

When It's Moderate to Severe (Painful or big area):

If there is severe pain, pressure, or big black area:
Step 1: Release Pressure (Trephination)

• It should be done within 24–48 hours of trauma, if possible, by a medical professional.
• A small puncture is created in the nail (with a sterile needle, hot instrument, or laser) to let out the blood that has become trapped.
• It relieves pain right away.
• Do not try this at home unless you are qualified — incorrect technique may lead to infection or further damage.

Step 2: Aftercare

• Immerse in warm soapy water 1–2 times a day for 10–15 minutes.
• Keep it clean and covered.
• Watch for signs of infection (redness, pus, swelling, pain).
• OTC analgesics such as ibuprofen or acetaminophen may alleviate pain.

How to diagnose black spot on nail?

Diagnosis of a black spot on a nail is a step-by-step process considering appearance, history, and occasionally other tests.

Step-By-Step Diagnosis of Black Spot on the Nail:

Detailed History

A doctor will inquire:

• When did you first see it?
• Did you hurt the nail or finger/toe?
• Has the spot increased in size, changed color, or shape?
• Is it painful?
• Is it spreading to adjacent skin?
• Any history of personal or family history of skin cancer?

Visual Examination

They'll examine:

• Location: Under the nail, within the nail plate, or extending to surrounding skin?
• Size & Shape: Is the lesion round, linear (stripe), or irregular?
• Color: Solid black, brown, red, purple?
• Nails involved: One nail versus multiple nails.

Other Diagnostic Aids

Dermatoscopy (Nail Dermoscopy)

• A dermatoscope enlarges and illuminates the nail to assess pigment pattern.
• Assists to differentiate benign melanonychia from melanoma.

Nail Biopsy (if suspicious)

• A small nail matrix or bed is removed.
• This is the only absolute method to diagnose melanoma or exclude dangerous conditions.

Nail Clipping & Lab Tests

• Nail clippings can be sent for fungal culture or microscopy if a fungal infection is suspected.

Fungal Infection on Nails

A fungal infection of the nail (medical jargon: onychomycosis) is a prevalent disease in which fungi infect the nail, typically beginning at the tip and spreading inward. It is less likely to occur in fingernails but more likely in toenails, as they have more exposure to moisture and less ventilation.

Causes of Nail Fungal Infections

• Dermatophytes (most common)
• Yeasts (such as Candida)
• Molds

These microorganisms love warm and moist environments such as sweaty socks, gymnasium floors, and communal showers.

Black Streak on Nail

A black stripe on the nail, particularly one which is vertical from base (cuticle) to end, is a medical term known as longitudinal melanonychia. This may have benign or severe reasons behind it, so careful consideration is needed.

Potential Reasons for a Black Stripe on a Nail

Benign (Non-threatening) Reasons

Melanonychia due to excess melanin

• More prevalent in individuals with darker skin
• Generally harmless
• May occur on many nails

Nail Trauma

• Chronic pressure (tightly worn shoes, biting of the nail, etc.)
• Causes release of pigment or bleeding (subungual hematoma) that can appear as a streak

Fungal Infection

• Rarely shows as a dark streak
• Typically with thickening or discoloration

Medications

• Some medications (e.g., chemotherapy, antimalarial drugs) cause pigmentation

Benign mole (nail matrix nevus)

• Constant in size
• Typically appears in young individuals

Serious Cause: Subungual Melanoma

• A rare but fatal skin cancer beneath the nail, most commonly occurring as:
• One, dark brown or black streak
• Widening, darkening, or irregular borders
• Pigment spread to nearby skin (Hutchinson's sign)
• No trauma
• Can eventually lead to nail cracking, lifting, or bleeding

When to worry about nail discoloration?

Discoloration of the nail is frequent and usually benign, but in some instances, it may indicate underlying conditions, such as infections or even cancer. The following is a guide to when to be concerned:

Black/Brown Stripe

• Subungual melanoma or trauma
• Single nail only, widening or irregular stripe, pigment on skin fold (Hutchinson's sign)

Green

• Bacterial infection (Pseudomonas)
• Nail is smelly, discolored, separates from nail bed

Yellow/Thickened

• Fungal infection, lung disease, diabetes
• Nail crumbles, thickens, or smells

White patches or spots

• Leukonychia (injury or minor issue)
• Concern if persistent, increasing, or in all nails

Blue or purple

• Poor blood flow, cyanosis, heart/lung problem
• Nail appears blue even at warm temperature

Red or brown beneath nail

• Splinter hemorrhages (bleeding)
• Multiple nails + fever may indicate endocarditis

Half white, half brown (Terry's nails)

• Liver or kidney disease
• Affects all nails, acute onset

Grey or darkened nails

• Medication side effect or systemic disease
• Sudden onset, extending to skin

Nail Cancer Early Signs

Early warning signs of nail cancer — especially subungual melanoma, the most severe form — is subtle and may be misdiagnosed as a bruise, fungus, or mole. But early diagnosis is key, so it's helpful to know what to watch for in order to save lives.

• Dark Stripe or Band (Longitudinal Melanonychia)
• Irregular Appearance
• Pigment on Skin Near the Nail
• No History of Trauma
• Changes Over Time
• Nail Changes

Black Spot on Nail Bed

A black discoloration of the nail bed is commonly due to small injury (subungual hematoma), fungal infection, or benign pigmentation such as melanonychia, particularly if it's fixed and painless. But if the discoloration occurs without trauma, enlarges, darkens, extends to adjacent skin, or produces distortion or pain of the nail, it may be an indication of subungual melanoma, a rare but dangerous nail cancer.

Dermatologist for Nail Problems

• Dr. Monica Bambroo, Artemis Hospital, Gurgaon
• Dr. Sheilly Kapoor, Medanta-The Medicity, Gurgaon
• Dr. Naresh Jain, Fortis Memorial Research Institute, Gurgaon
• Dr. Anju Mangla, Apollo Hospital, Delhi