Nail discoloration under the nail can be harmless, but it can also signal infection, injury, or an underlying medical condition.
This guide explains what causes nail discoloration under the nail and which color changes deserve prompt attention.
What does discoloration under the nail mean?
Discoloration under the nail refers to a change in color in the nail plate, nail bed, or the space beneath the nail.
The appearance may be white, yellow, brown, green, red, purple, or black, and the pattern can help narrow down the cause.
Some changes develop slowly from repeated pressure or chronic skin conditions.
Others appear suddenly after trauma, bleeding, or infection.
The nail may also become thick, brittle, lifted, painful, or foul-smelling depending on the cause.
What causes nail discoloration under the nail?
Several conditions can change the color beneath a fingernail or toenail.
The most common causes include infection, trauma, inflammation, pigment changes, and less commonly, serious disease.
1. Injury or bleeding under the nail
A direct hit to the nail can cause blood to collect under it, creating a dark red, purple, or black area called a subungual hematoma.
This often follows dropping something on the toe, stubbing a toe, or repetitive pressure from tight shoes or running.
The discoloration usually appears shortly after the injury and may be painful or throbbing.
As the nail grows, the blood spot typically moves outward with the nail.
2. Fungal nail infection
Onychomycosis is one of the most common causes of yellow, white, or brown nail discoloration.
The nail may also thicken, become crumbly, and separate from the nail bed.
Fungal infections are more common in toenails than fingernails and are often associated with sweaty feet, communal showers, nail trauma, diabetes, or poor circulation.
Dermatophytes are the most frequent organisms, though yeasts and molds can also be involved.
3. Bacterial infection
Bacteria can discolor the nail, especially if the nail is lifted or damaged.
A greenish tint often points to Pseudomonas infection, which can occur when moisture gets trapped under a partially detached nail.
Bacterial infections may cause odor, tenderness, swelling, or drainage.
They are more likely when the nail is repeatedly wet, artificially enhanced, or already damaged by trauma or fungus.
4. Psoriasis and other inflammatory skin conditions
Nail psoriasis can create yellow-brown discoloration, pitting, thickening, and lifting from the nail bed.
The classic “oil drop” or “salmon patch” can look like a translucent yellowish spot beneath the nail plate.
Eczema and lichen planus can also alter nail color and texture.
These conditions may affect one nail or many, and they often occur alongside skin rash, scalp scale, or joint symptoms.
5. Melanonychia and pigment changes
Melanonychia is brown or black pigmentation in the nail caused by melanin.
It may appear as a narrow band or broader discoloration and can be normal in people with darker skin tones.
Common benign triggers include pregnancy, certain medications, friction, and ethnic pigmentation.
However, a new, changing, or irregular dark band in a single nail should be evaluated because it can occasionally indicate subungual melanoma.
6. Medication side effects
Some medicines can change nail color or alter the way the nail grows.
Examples include certain chemotherapy drugs, antimalarials, tetracycline-class antibiotics, minocycline, and drugs that affect pigment or circulation.
Medication-related nail changes may affect several nails at once and can come with other side effects such as skin discoloration, fatigue, or photosensitivity.
7. Subungual melanoma
Although uncommon, melanoma under the nail is a critical cause to rule out when dark discoloration is new, irregular, or enlarging.
It may start as a brown or black streak, a patch, or pigment spreading to the surrounding skin around the nail.
Warning signs include one nail being affected, a band that widens toward the base, nail splitting, pigment on the cuticle, or no clear history of trauma.
Early diagnosis matters because subungual melanoma can be overlooked for months.
8. Nutritional or systemic conditions
Less commonly, nail discoloration can be linked to systemic disease such as liver disease, kidney disease, thyroid disorders, anemia, or vascular problems.
Deficiencies in iron, vitamin B12, or protein may also affect nail appearance.
In these cases, the nail color change is often accompanied by other symptoms like fatigue, swelling, skin color changes, hair loss, or changes in nail growth across multiple nails.
Which nail colors point to specific causes?
The color and pattern of the change often provide useful clues:
- Yellow: fungal infection, psoriasis, nail thickening, smoking, or medication effects
- Green: bacterial infection, especially Pseudomonas
- Brown or black: bruising, melanonychia, melanoma, or staining from chemicals
- White: surface injury, fungal infection, or nail plate separation
- Red or purple: recent bleeding beneath the nail after trauma
Pattern matters as much as color.
A stable, symmetrical change in several nails is more often benign or systemic, while a new change in one nail needs closer attention.
When should nail discoloration be evaluated?
Medical evaluation is important if the discoloration is new, painful, spreading, or not clearly linked to an injury.
You should also get checked if the nail is lifting, draining, thickening rapidly, or changing shape.
Prompt assessment is especially important if you notice any of the following:
- A dark streak or spot that changes in size or color
- Pigment extending onto the skin around the nail
- Bleeding without obvious trauma
- Persistent pain, swelling, or pus
- Discoloration in a single nail with no clear cause
- Nail destruction in someone with diabetes or poor circulation
How do clinicians diagnose the cause?
Diagnosis starts with a history and physical exam.
A clinician may ask about recent injury, footwear, sports activity, manicures, medication use, skin disease, and whether the problem affects one nail or several.
Depending on the appearance, the evaluation may include a fungal culture, nail scraping, dermoscopy, bacterial testing, or a biopsy.
When melanoma is a concern, a nail matrix biopsy may be needed to examine the pigment source directly.
What can you do at home while waiting for care?
Home care depends on the cause, but a few safe steps can help protect the nail:
- Keep the area clean and dry
- Avoid picking, cutting, or drilling into the nail
- Wear roomy shoes if a toenail is painful
- Trim the nail straight across if it is not detached
- Pause nail polish if you need to monitor color changes
- Seek care sooner if pain, redness, or drainage develops
If the discoloration follows a minor injury and there is no severe pain, the spot may simply grow out over time.
If the cause is uncertain, especially with dark pigment, waiting too long can delay important treatment.
How to reduce the risk of future nail discoloration
Not all nail discoloration is preventable, but risk can be lowered by protecting the nails from trauma and moisture.
Good foot hygiene, dry socks, properly fitting shoes, and avoiding repeated chemical exposure all help.
For people prone to fungal infections, treating athlete’s foot early, not sharing nail tools, and disinfecting clippers can reduce recurrence.
For those with psoriasis or eczema, controlling the underlying skin disease often improves nail appearance as well.
If discoloration keeps returning or affects multiple nails, an underlying condition may need long-term management rather than repeated self-treatment.