Toenail discoloration can be harmless, temporary, or a sign of an underlying health issue.
Understanding what causes toenail discoloration helps you tell the difference between a minor stain and a change that deserves medical evaluation.
What causes toenail discoloration?
Toenail color changes happen when pigment, blood, infection, trauma, or tissue damage affects the nail plate or the nail bed underneath it.
In many cases, the cause is local to the nail, but some changes reflect systemic conditions such as diabetes, peripheral vascular disease, liver disease, or nutritional deficiencies.
The appearance matters: discoloration may be yellow, white, brown, black, green, blue, or even red.
Each color pattern points to different likely causes, and the texture, thickness, and speed of change provide additional clues.
Common causes of toenail discoloration
1. Fungal nail infection
Onychomycosis is one of the most common reasons toenails turn yellow, white, or brown.
The nail often becomes thickened, brittle, crumbly, or distorted, and debris can collect under the nail edge.
Fungal infections usually develop slowly and are more likely in people who wear tight shoes, have sweaty feet, use communal showers, or have a history of athlete’s foot.
Toenails are more commonly affected than fingernails because feet spend more time in warm, moist environments.
2. Repeated trauma or pressure
Stubbing the toe, running long distances, or wearing shoes that rub can cause the nail to discolor from bleeding beneath the nail plate.
This is often called a subungual hematoma.
The color may look red, purple, dark brown, or black and typically appears after an injury.
Chronic pressure can also make nails look white, yellow, or bruised over time.
Athletes, dancers, hikers, and people with poorly fitting footwear are at higher risk.
3. Nail polish and cosmetic staining
Dark nail polish, especially without a base coat, can stain the keratin of the nail and create a yellow-brown tint.
This is usually harmless and improves as the nail grows out.
Harsh removers and frequent polish use may also dry the nail and make discoloration more noticeable.
4. Bacterial infection
Some bacterial infections, including Pseudomonas, can turn the nail greenish or green-black.
This often occurs when the nail lifts slightly from the nail bed, allowing moisture to collect underneath.
Bacterial discoloration may be accompanied by odor, tenderness, swelling, or drainage, especially if the surrounding skin is also irritated.
5. Psoriasis and other inflammatory skin conditions
Nail psoriasis can cause pitting, thickening, lifting, and a yellow-brown discoloration known as the “oil drop” sign.
Eczema, lichen planus, and other inflammatory disorders may also change the color and surface of the nail.
These conditions often affect several nails and may occur alongside skin plaques, scalp flaking, or joint pain.
6. Circulation problems
Poor circulation can change nail color because less oxygen-rich blood reaches the toes.
Conditions such as peripheral artery disease, Raynaud phenomenon, and other vascular disorders may cause pale, bluish, or dusky nails, especially when the feet are cold.
These changes are more concerning when they are persistent, painful, or associated with numbness, cold feet, or non-healing wounds.
7. Medication side effects
Certain medications can cause nail pigmentation.
Tetracycline antibiotics, antimalarial drugs, chemotherapy agents, and some medications used for inflammatory or cardiac conditions may create brown, blue-gray, or black streaking or diffuse discoloration.
If discoloration begins after starting a new medication, a clinician can help determine whether it is a known side effect or a separate problem.
8. Nutritional deficiencies and systemic illness
Iron deficiency, vitamin B12 deficiency, thyroid disorders, liver disease, kidney disease, and diabetes can affect nail growth, strength, and color.
These changes are often subtle and may include brittleness, ridging, thickening, or pale nail beds.
Because nails grow slowly, systemic issues may show up gradually and affect multiple nails rather than just one.
When toenail discoloration may be serious
Some discoloration is cosmetic, but certain patterns need prompt medical attention.
A single dark streak, especially one that widens or changes over time, should be evaluated to rule out melanoma under the nail.
New black discoloration without a clear injury also deserves assessment.
You should seek medical care if discoloration is accompanied by any of the following:
- Pain, swelling, warmth, or pus around the nail
- A nail that is lifting, splitting, or becoming deformed
- Rapidly spreading redness or skin infection
- Dark pigment extending onto the surrounding skin
- Discoloration after an injury with severe pain or pressure
- Multiple nail changes along with fatigue, weight loss, or other systemic symptoms
How clinicians diagnose the cause
Diagnosis starts with a visual exam and a medical history.
A clinician may ask when the color changed, whether there was trauma, what shoes you wear, whether you have athlete’s foot, and whether you have conditions such as diabetes or psoriasis.
If fungus is suspected, a nail clipping or scraping may be sent for microscopy, culture, or polymerase chain reaction testing.
If pigmentation is concerning, a dermatologist may use dermoscopy or recommend a biopsy.
When circulation or systemic disease is suspected, blood tests or vascular studies may be ordered.
What you can do at home
Home care depends on the cause.
For mild staining from polish, allow the nail to grow out and avoid repeated harsh removers.
For pressure-related discoloration, switch to wider toe boxes and trim nails straight across to reduce repeated trauma.
If fungus is likely, keep feet clean and dry, change socks regularly, and avoid sharing nail tools.
Over-the-counter antifungal creams may help athlete’s foot, but nail fungus often requires prescription treatment because topical products penetrate the nail poorly.
Do not try to dig under the nail or scrape away dark pigment.
That can worsen injury and increase infection risk.
How to reduce the risk of toenail discoloration
- Wear properly fitting shoes with enough room in the toe box
- Keep feet dry and change socks after exercise
- Use shower sandals in gyms, pools, and locker rooms
- Trim nails straight across and avoid cutting them too short
- Disinfect nail tools and do not share clippers
- Treat athlete’s foot early to prevent spread to the nails
- Protect toes during sports and repetitive-impact activities
What yellow, green, brown, and black toenail colors usually suggest
Yellow toenails
Yellow discoloration often points to fungal infection, polish staining, or chronic pressure.
In some cases, it may reflect nail psoriasis or slower nail growth with age.
Green toenails
Green color is commonly associated with bacterial infection, particularly when moisture is trapped under a lifted nail.
Brown toenails
Brown discoloration can come from trauma, fungal infection, medication staining, or pigment changes that need closer examination.
Black toenails
Black discoloration may be caused by bruising under the nail, but it can also signal a more serious condition.
If there is no obvious injury or the dark area does not grow out with the nail, it should be checked by a clinician.
Which specialists treat toenail discoloration?
A primary care clinician can evaluate many causes of toenail discoloration, especially when infection, trauma, or circulation problems are suspected.
Dermatologists treat nail disorders, skin diseases, and concerning pigment changes.
Podiatrists can help with nail trauma, structural foot problems, and fungal management.
If the issue is related to diabetes, vascular disease, or another systemic condition, coordinated care may be needed to address both the nail and the underlying cause.