Why Are My Nails Turning Black?
Black or darkened nails can be alarming, especially when the color change appears suddenly or affects only one nail.
In many cases, the cause is minor and treatable, but in some situations it can signal an underlying health problem that needs prompt medical attention.
The key is to look at patterns: how many nails are affected, whether there was injury, and whether the discoloration is changing over time.
That context can help narrow down the most likely cause.
Common Causes of Black Nails
Several conditions can turn a nail black or dark brown.
The most common explanations involve bleeding under the nail, pigment changes, infection, or medication effects.
1. Trauma or a Subungual Hematoma
A blow to the finger or toe can cause blood to collect under the nail, creating a dark purple, red, or black spot known as a subungual hematoma.
This is one of the most common reasons for sudden nail discoloration.
Typical triggers include:
- Dropping something heavy on the nail
- Stubbing a toe
- Repetitive pressure from tight shoes
- Sports injuries such as running or hiking
In these cases, the nail may also throb, feel tender, or lift as it grows out.
As the nail grows, the discoloration usually moves outward over weeks or months.
2. Fungal Nail Infection
Onychomycosis, or fungal nail infection, usually causes yellow, white, or brown discoloration, but severe infections can make the nail appear dark.
The nail may become thickened, brittle, crumbly, or distorted.
Fungal infections are more likely in warm, moist environments and can affect toenails more often than fingernails.
They tend to develop slowly rather than appearing overnight.
3. Pigment Changes and Melanonychia
Melanonychia refers to brown or black pigment in the nail plate.
It can be caused by normal pigmentation, repeated friction, certain medications, inflammatory skin conditions, or melanoma.
A single dark stripe or a changing dark area should always be evaluated carefully.
Causes of melanonychia include:
- Normal ethnic pigmentation, especially in darker skin tones
- Repeated nail trauma
- Psoriasis or lichen planus
- Certain chemotherapy drugs and other medications
- Melanocytic lesions, including melanoma
4. Melanoma Under the Nail
Subungual melanoma is a rare but serious form of skin cancer that can appear as a black or brown streak, a dark patch, or a nail that seems to split or lift.
It may begin as subtle discoloration and is often mistaken for trauma or fungal disease.
Warning signs can include:
- A dark stripe that widens over time
- Irregular color or border
- Pigment extending onto the surrounding skin
- One nail affected without a clear injury
- Bleeding, pain, or nail destruction
Any persistent, unexplained dark nail should be checked by a dermatologist, especially if it is changing.
5. Infections Caused by Bacteria or Yeast
Although less common than fungal infections, bacterial or yeast infections can darken the nail or the skin around it.
Pseudomonas bacteria can create a green-black discoloration, particularly in nails that are lifted or exposed to moisture.
These infections are more likely if the nail is already damaged, artificial nails are present, or the hands are frequently wet.
6. Medication Side Effects
Some medications can cause dark bands or diffuse nail discoloration.
Chemotherapy drugs are a well-known cause, but other medications may also contribute to pigment changes in the nails.
If the color change started after beginning a new drug, do not stop the medication on your own.
A clinician can determine whether the nail change is expected or requires further evaluation.
What Black Nail Color Can Tell You
The appearance of the discoloration offers important clues.
A flat dark spot after an injury usually points to bleeding under the nail, while a slowly developing stripe may suggest pigment deposition.
Thickening and crumbling are more consistent with infection, and irregular pigment that spreads can be more concerning.
Consider these pattern clues:
- One nail only: trauma, melanoma, or localized infection
- Multiple nails: medication effects, systemic disease, or repeated pressure
- Painful and sudden: subungual hematoma or acute infection
- Slowly changing: fungal infection, melanonychia, or melanoma
Other Symptoms That Matter
Black nails are not always isolated.
Additional symptoms can help identify the cause and indicate whether the problem is urgent.
- Pain or throbbing: often suggests trauma or pressure under the nail
- Swelling and redness: may point to infection or inflammation
- Bad odor or drainage: can indicate bacterial infection
- Nail lifting or splitting: common with trauma or fungal disease
- Skin pigment around the nail: a red flag for possible melanoma
When Should You See a Doctor?
You should seek medical evaluation if the cause is unclear, the discoloration is growing, or there is no history of injury.
A dermatologist or primary care clinician can examine the nail and decide whether testing, imaging, or biopsy is needed.
Get prompt medical care if:
- The nail is black without an obvious injury
- The discoloration is a new dark streak or patch
- Pigment extends onto the cuticle or surrounding skin
- The nail is painful, swollen, or draining
- The nail is thick, crumbling, or separating from the nail bed
- You have diabetes, poor circulation, or a weakened immune system
How Doctors Diagnose Black Nails
Diagnosis usually starts with a physical exam and a review of your symptoms, footwear, injuries, medications, and medical history.
If infection is suspected, the clinician may trim a small sample of nail for microscopy or culture.
If melanoma is a concern, the doctor may perform dermoscopy or recommend a nail matrix biopsy.
The goal is to distinguish harmless pigment changes from conditions that need treatment.
Treatment Options
Treatment depends on the cause.
A subungual hematoma may only need monitoring if pain is mild, though severe pressure sometimes requires drainage soon after injury.
Fungal infections are usually treated with topical or oral antifungal medication, and bacterial infections may need antiseptics or antibiotics.
For pigment changes related to medication or inflammation, treatment focuses on the underlying trigger.
If melanoma is suspected, rapid referral to a dermatologist or surgical specialist is essential.
What You Can Do at Home
Home care may help if the cause is clearly a minor injury and the nail is not severely painful.
Keep the area clean, protect the nail from further trauma, and wear comfortable shoes if a toenail is affected.
Helpful steps include:
- Apply ice soon after an injury to reduce swelling
- Elevate the hand or foot when possible
- Avoid picking at a lifted nail
- Keep nails trimmed and dry
- Wear shoes with enough toe room
If the discoloration does not grow out with the nail or continues to change, it should be examined.
How to Reduce the Risk of Nail Discoloration
Good nail care can lower the risk of trauma and infection.
Trim nails straight across, avoid very tight shoes, and protect hands and feet during activities with high impact or repetitive pressure.
For people prone to fungal infections, keeping feet dry, changing socks regularly, and disinfecting nail tools can help.
If you use acrylic or gel nails, be careful about nail damage and moisture trapped beneath the enhancement.
Why the Cause Matters
A black nail is often harmless when it follows a clear injury, but the same appearance can also signal melanoma, infection, or another condition that should not be ignored.
Paying attention to timing, texture, symptoms, and whether the color is spreading can help determine the next step.
If you are still asking why are my nails turning black and there is no clear explanation, a medical exam is the safest way to find out what is happening.