By Dr. Evan Lewis, PhD
Last updated: 9 August 2026
Discolored toenails are most often caused by a fungal infection, but trauma, nail polish staining, a nutrient deficiency and psoriasis all look similar at a glance. The colour, where it started, and whether the nail has thickened are the three things that tell them apart.
This guide covers what causes discolored toenails, what actually helps for each cause, and when it is time to see a doctor.
What causes discolored toenails?
Six causes account for almost all of it: fungal infection, bacterial infection, trauma, nutrient deficiency, a systemic condition, and cosmetic staining from polish. Here is how each one presents.
1. Fungal Infection (Onychomycosis)
Fungal infection, clinically known as onychomycosis, is the leading cause of discolored toenails worldwide. A 2019 review by Gupta and Versteeg put the prevalence of superficial fungal infections of the feet at somewhere between 10% and 53% depending on the population studied (PubMed 29521517). Nails affected this way are typically yellow, brown, or opaque white, often with a chalky or crumbly texture along the edges.
Fungi thrive in warm, moist environments. The inside of a closed shoe creates exactly the right conditions for fungal overgrowth. Infections are commonly picked up in:
- Public swimming pools and showers
- Gym locker rooms
- Nail salons with inadequately sanitized tools
- Direct contact with an infected person's nails
Household spread matters more than most people expect. A 2022 scoping review in J Fungi found onychomycosis and dermatophytosis pass between household members, which is why towels, bath mats and nail clippers are worth keeping separate (Jazdarehee et al., PubMed 35050000).
Left alone, fungal toenail infections tend to worsen. The nail can become thickened, brittle, and even separate from the nail bed. Acting early is easier than acting late.
Signs of fungal toenail infection:
- Yellow, white, or brown nail discoloration
- Thickened or brittle nail
- Chalky or powdery texture
- Nail separating from the nail bed (onycholysis)
- Mild odour coming from the affected nail
2. Bacterial Infection
Bacterial infections are a less common but equally important cause of toenail discoloration. They typically enter through a break in the skin near the nail: a small cut, ingrown toenail, or cracked cuticle. Pseudomonas bacteria, for example, can produce a characteristic green-black discoloration under the nail, sometimes accompanied by pain, swelling, or an unpleasant smell.
Unlike fungal infections, bacterial nail infections often develop quickly and may involve surrounding skin redness or warmth. If you are not sure which one you are looking at, here is how to tell a bacterial nail infection from a fungal one.
3. Trauma and Subungual Hematoma
Stubbing your toe, dropping something heavy on your foot, or wearing tight shoes during long runs can all cause bleeding beneath the nail, called a subungual hematoma. This trapped blood appears dark purple or black under the nail and can be alarming to see for the first time.
In most cases, trauma-related nail discoloration is not dangerous. The darkened portion will gradually grow out over several weeks or months as the nail advances. However, if the injury is severe or particularly painful, a doctor can safely drain the pressure.
Runners and athletes frequently experience this type of discoloration due to repetitive pressure on the nail from ill-fitting footwear.
4. Vitamin and Mineral Deficiency
Your nails are made of keratin, a protein that depends on a steady supply of vitamins and minerals to form properly. Deficiencies in certain nutrients can cause noticeable changes in nail colour and texture:
- Iron deficiency: can cause pale, spoon-shaped nails (koilonychia)
- Vitamin B12 deficiency: associated with bluish or brownish nail discoloration
- Zinc deficiency: linked to white spots and slow nail growth
- Biotin deficiency: can lead to brittle nails that chip and break easily
If your nails have changed colour without any obvious injury or infection, it's worth asking your doctor for a comprehensive blood panel.
5. Underlying Medical Conditions
Systemic health conditions can manifest in the nails before other symptoms become obvious. Some conditions associated with toenail discoloration include:
- Psoriasis: causes pitting, separation, and yellow-brown discoloration
- Lichen planus: can cause nail thinning, ridging, and darkening
- Peripheral artery disease: reduced circulation can slow nail growth and cause yellowing
- Diabetes: impairs immune response and circulation, increasing susceptibility to fungal infection
- Lung or liver disease: certain patterns of nail discoloration (such as Terry's nails, white with a narrow pink band at the tip) can indicate organ dysfunction
If your nail discoloration is accompanied by other unexplained symptoms, consult a healthcare professional promptly.
6. Nail Polish and Cosmetic Staining
Prolonged use of dark nail polish, especially without a protective base coat, can leave behind yellowish staining on the nail surface. This type of discoloration is superficial and cosmetic, not a sign of infection. Allowing the nail to breathe between polish applications typically resolves it over time.
How do you fix discolored toenails?
It depends entirely on the cause, and on patience. Whatever you use, the discoloured part of the nail does not change colour. It has to grow out. Toenails grow at roughly 1.62mm a month (Yaemsiri, JEADV 2010, PubMed 19744178), and a great toenail is 20 to 25mm long, so a full grow-out takes 12 to 18 months. Ninety days of consistent care buys you about 5mm of new nail at the base. That is what progress actually looks like.
For fungal infections: daily topical care
Topical antifungal products are the usual first step for mild-to-moderate fungal toenail infections. These come as creams, nail lacquers, and iodine-based sprays. Consistency matters more than potency: most protocols need daily use for several months while the nail slowly grows out.
Iodine-based solutions have a long history of use in wound care and skin surface care. Our walkthrough of what the research actually shows about iodine and nail fungus covers the three published papers on iodine applied to onychomycosis-affected nails, and what they do and do not establish.
For severe or persistent cases, a dermatologist may prescribe oral antifungal medications. These carry a higher risk of side effects and require monitoring.
For bacterial infections: keep it clean and seek care
Bacterial nail infections typically require a course of antibiotics prescribed by a physician. While waiting for your appointment, keep the area clean and dry, avoid picking at the nail or surrounding skin, and cover with a sterile dressing if there is any open wound.
For trauma-related discoloration: wait it out
Most trauma-related nail discoloration resolves on its own as the nail grows. Avoid wearing tight footwear, keep the nail trimmed straight across, and monitor for signs of secondary infection (increasing pain, redness, or discharge). If the pressure is severe, a doctor can safely relieve it.
For nutritional deficiencies: targeted supplementation
If a blood test reveals a deficiency, targeted supplementation under medical guidance can gradually restore healthy nail growth. Biotin (vitamin B7) is particularly well-studied for improving nail strength and appearance. Iron, zinc, and B12 supplements can also help when deficiency is confirmed.
For underlying medical conditions: address the root cause
When nail discoloration is a symptom of psoriasis, diabetes, or another systemic condition, the most useful thing is managing that condition. Speak with your doctor, and use supportive foot care to look after nail health in the meantime.
Daily foot hygiene habits
Good foot hygiene is one of the most underrated parts of looking after discoloured nails. Key habits include:
- Wash feet daily with soap and water, paying attention to the spaces between toes
- Dry feet thoroughly after bathing or swimming, especially between toes
- Wear moisture-wicking socks and breathable footwear
- Wear sandals or water shoes in public showers, pools, and locker rooms
- Trim toenails straight across and keep them at a moderate length
- Avoid sharing nail tools, socks, or footwear
- Rotate shoes to allow full drying between wears
When should you see a doctor?
Most cases of discolored toenails are manageable at home, but certain signs warrant prompt medical attention:
- The nail is causing significant pain or throbbing
- There is swelling, redness, or warmth around the nail (signs of active infection)
- The nail has completely separated from the nail bed
- You have diabetes, poor circulation, or a compromised immune system
- A dark streak runs from the nail tip to the cuticle (could indicate melanoma)
- Home care has not improved the nail after 3 to 4 months
Dark streaks under the nail, especially if they expand over time, should always be evaluated by a dermatologist to rule out subungual melanoma, a rare but serious condition.
What does a daily nail routine look like?
Two steps, done every day, for long enough to matter. The IodinePure EZ Clear Nails Kit is built around that: soak three to four times a week using the foot tray, and spray the nail, the nail edges and the surrounding skin twice daily in between. Soak. Spray. Repeat.
It is a two-ingredient aqueous iodine formula, listed with Health Canada as a cosmetic, and it is used daily in over 200 foot care clinics across North America. It does not stain, sting or dry the skin, which is the practical reason people manage to keep using it.
Who it is not for: anyone with a known iodine sensitivity or a thyroid condition their doctor is managing, and anyone hoping the discoloured part of the existing nail will change colour. It will not. Only the new nail growing from the base comes in clear, and that takes the 12 to 18 months described above.
For related reading, see our guides on types of toenail fungus and using iodine for toenail fungus.
Frequently Asked Questions About Discolored Toenails
What is the most common cause of discolored toenails?
Fungal infection (onychomycosis) is the most common cause of toenail discoloration. It typically causes yellow, brown, or white nail discoloration, often accompanied by thickening or brittleness. Warm, moist environments like the inside of shoes create ideal conditions for fungal growth.
Can discolored toenails go away on their own?
It depends on the cause. Trauma-related discoloration typically grows out on its own over several weeks. Cosmetic staining from nail polish may fade once polish is removed. Fungal infections rarely resolve on their own and tend to worsen over time without consistent care.
How do you fix discolored toenails caused by fungus?
With daily topical care and time. Iodine-based sprays and nail lacquers are the usual first approach for mild-to-moderate fungal nail discoloration, applied daily alongside a foot soak three to four times a week. The discoloured nail itself does not change colour; only the new nail growing from the base comes in clear, which takes 12 to 18 months for a full toenail.
Can nail polish cause toenail discoloration?
Yes. Prolonged use of dark nail polish without a base coat can leave yellowish staining on the nail surface. This is a superficial cosmetic issue, not an infection. Taking breaks between polish applications and always using a base coat keeps it from happening.
Is it safe to get a pedicure if I have discolored toenails?
If your discoloration is caused by a fungal infection, it is best to avoid a pedicure until the nail has recovered, since shared tools and water can pass it on. If you do visit a salon, inform the technician, bring your own nail tools, and ensure all equipment is properly sanitized.
Dr. Evan Lewis, PhD, specializes in natural and nutritional therapies for the prevention and management of chronic diseases and their complications. His research spans chronic disease, diabetes complications, clinical nutrition, and nerve health, including the development of topical iodine approaches for foot care and wound health. IodinePure products are listed with Health Canada as cosmetics.
