A close-up shot of elegantly manicured black nails adorned with a sleek and precise white line running along the tips, exuding sophistication and modernity.

Black Nails With White Lines: Causes And Treatment

If you’ve noticed mysterious white lines on your black painted nails, you may be wondering what’s causing them and whether you should be concerned. These white lines and spots are actually quite common and usually harmless.

If you’re short on time, here’s a quick answer to your question: The white lines on black nails are caused by minor trauma to the nail that reveals the natural nail underneath the polish. They are generally harmless and can be avoided by using a base coat under dark nail polish.

In this comprehensive guide, we’ll explore the common causes of white lines on black nails, when you should see a doctor, treatment options, prevention tips, and answer related questions.

What Causes White Lines on Black Nails

Minor Trauma to the Nail

One of the most common causes of white lines or spots on the nails is minor injuries or trauma to the nail. This can happen from things like hitting your nail against a hard surface, jamming your finger in a door, or dropping something on your nail.

When trauma occurs, it causes a temporary stop in nail growth in the area that was injured. As the nail continues to grow out, this results in a white spot or line on the nail where there was disrupted growth.

These white spots or lines are harmless and will grow out as your nail grows. They are generally referred to as “leukonychia” by dermatologists. While leukonychia can be caused by conditions like zinc deficiency, the type caused by trauma is the most common.

Thinning Nail Polish

Using nail polish, especially dark colors like black, for extended periods of time can also lead to white lines on the nails. As the polish thins out towards the tip of the nail, the thinned area allows more light to pass through showing the white of the nail underneath.

So this gives the appearance of a white line near the tip of the nail.

To avoid this, make sure to regularly remove polish and give your nails a break in between reapplications. Removing polish completely and allowing it to re-grow out can make these lines disappear.

Fungal Infections (Rare)

While less common, fungal infections can also cause white or yellow nails in some cases. A fungal infection occurs when fungi overgrow under and inside the nail. One type of fungal infection called distal subungual onychomycosis specifically causes white spots on the tips of nails.

If you suspect you may have a fungal nail infection, it’s best to see a dermatologist. They can examine your nails and may take a sample for testing. Fungal nail infections require prescription antifungal medication, both oral and topical, to clear up.

When to See a Doctor

Black lines on the nails can sometimes be a harmless condition, but they may also indicate an underlying medical issue. It’s important to see your doctor if you notice any of the following:

  • The lines are getting darker or wider
  • New black lines are appearing
  • The lines are accompanied by changes in nail texture or color
  • You have other symptoms like pain, swelling, or discharge around the nail

Seeing your doctor promptly can allow early diagnosis and treatment of issues like melanoma (a type of skin cancer), nail fungus, or systemic disorders affecting nail growth. Some warning signs that warrant urgent evaluation include:

  • Very dark black or brown lines that look “stuck” under the nail and do not grow out with the nail
  • Lines accompanied by nail crumbling, thickening, loosening, or detachment
  • Redness, throbbing pain, bleeding, or pus around the nail

When you visit the doctor, be prepared to discuss:

  • When you first noticed the lines and any changes you’ve observed over time
  • Which nails are affected
  • Any injuries or other symptoms involving the nails or fingers/toes
  • Your medical history and risk factors like family history, smoking, or past damage to the nails
  • All medications and supplements you currently take

Depending on the evaluation, your doctor may order blood tests or perform a nail biopsy to help diagnose the cause. With appropriate treatment guided by your doctor, many causes of black nail lines can be resolved.

How to Treat White Spots on Nails

Using a Base Coat

Applying a base coat before painting your nails is one of the most effective ways to prevent white spots from forming. The base coat creates a smooth, even surface that allows the color polish to glide on smoothly.

Look for a base coat that contains ingredients like vitamin E, biotin, and calcium, which can strengthen nails and reduce discoloration.

Be sure to apply the base coat to the entire nail, going all the way to the edges. Let it dry completely before painting color polish on top. Using a good base coat regularly can help reinforce the nail and prevent chipping or peeling that leads to white spots.

Applying Thicker Polish

Using multiple thin coats of polish often results in a streaky, uneven application that chips easily. Opting for an opaque, thicker polish means you may only need one or two coats for full, even coverage. The thicker consistency helps protect the nail and covers any existing white spots.

An opaque pastel polish or creme polish works best for achieving an evenly coated nail. Apply a thick stripe down the center of the nail, then fill out the sides until fully covered. Finish with a clear top coat to smooth and harden the manicure.

Addressing Underlying Causes

While base coats and polish tricks can help cover up white spots on nails, addressing the root cause is the best way to prevent them from recurring. Here are some common reasons white spots form and how to treat them:

  • Nutritional deficiencies – up your intake of biotin, zinc, iron, and calcium
  • Nail trauma – avoid picking at nails and use gloves for cleaning or gardening
  • Thyroid issues – see a doctor to get levels checked and treated
  • Fungal infection – use an over-the-counter antifungal polish or cream
  • Allergies – identify and avoid triggers that damage nails
  • Chemical exposure – wear gloves when using harsh soaps, detergents, or cleaning products

Paying attention to proper nail hygiene and care can also prevent white spots from occurring. Keep nails trimmed short, use cuticle oil daily, and avoid excessive water exposure. Be gentle when cleaning under and around nails.

If white spots on the nails persist despite trying these measures, visit a dermatologist to pinpoint and treat the underlying problem. With the right approach, you can get back to healthy, beautiful nails.

Prevention Tips

Avoid Picking at Nails

Picking at your nails can lead to damage and make you more prone to fungal infections or other issues that show up as white lines. Try to keep your hands busy with stress balls or fidget toys so you don’t mindlessly pick at your nails.

If you have the urge to pick, apply a no-bite bitter polish to deter yourself.

Use Gentle Nail Care

Be very gentle with your nails to prevent breakage and damage. Use a soft nail brush when cleaning under and around your nails, and opt for an acetone-free nail polish remover. When filing your nails, use gentle motions and avoid filing too aggressively at the edges and cuticles.

Consider applying a strengthening base coat or nail hardener to add a protective barrier.

Apply a Base Coat

Before polishing your nails, always apply a base coat first. Base coats help prevent nails from staining and can help smooth out nail imperfections. According to dermatologists at the American Academy of Dermatology Association (AAD), base coats add a layer of protection, preventing the pigments in nail polish from seeping into nails and causing stubborn stains.


Here are some frequently asked questions about black nails with white lines:

What causes black lines or stripes on nails?

Some common causes of black lines or stripes on nails include:

  • Melanonychia – This is a benign condition where there is increased production of melanin, the pigment that gives skin and hair their color, in the nails.
  • Subungual melanoma – This is a rare form of skin cancer that affects the nails. It can initially look like harmless melanonychia stripes.
  • Fungal infection – In some cases, a fungal nail infection can cause nails to darken and lines or spots to appear.
  • Medications – Certain medications like chemotherapy drugs can cause nails to darken or develop lines.
  • Trauma – Injury to the nail or frequent hitting or pressure can disrupt the nail growth and lead to black streaks.

Are black lines in nails always a sign of subungual melanoma?

No, most cases of dark nail lines are caused by harmless melanonychia. Only about 1-4% of melanonychia cases turn out to be subungual melanomas. However, it’s important to get checked by a doctor, especially if the lines are new, spreading fast, or you have other risk factors for melanoma.

How can you tell the difference between melanonychia and subungual melanoma?

There are a few key differences between benign melanonychia and early subungual melanoma:

Melanonychia Subungual Melanoma Signs
– Single thin black line – Dark black or brown line
– Uniform width of less than 3 mm – Irregular width, > 3-4 mm
– Linear, vertical orientation – Jagged, horizontal or oblique shape
– Not spreading quickly – Rapid growth over weeks/months

If you notice any of the warning signs for subungual melanoma, it’s important to see your doctor promptly for evaluation.

What’s the treatment for black lines on nails?

Treatment depends on the underlying cause:

  • Benign melanonychia often doesn’t need treatment beyond monitoring changes.
  • Fungal infections are treated with oral or topical antifungal medication.
  • Subungual melanomas are treated aggressively, usually with surgery to remove the affected nail and digits down to healthy tissue margins.

Dermatoscopy (exam under a special magnifying device) can help doctors evaluate suspicious nails and determine the need for biopsy.

Can you prevent black lines from forming on nails?

There’s no guaranteed way to prevent benign melanonychia stripes. However, protecting nails from injury/trauma, avoiding excessive pressure, wearing gloves for irritating chemicals/cleaners, and treating nail fungal infections promptly can help reduce risk.

Limiting UV light exposure may lower the risk of some rare cases of radiation-induced melanoma under nails.

Seeing your doctor right away if you notice any unusual nail changes is key, as early diagnosis leads to better outcomes if it does happen to be a subungual melanoma.


In most cases, white lines on black painted nails are harmless and simply signal minor trauma that exposes the natural nail. Using prevention tips like base coats and gentle nail care can help avoid lines from forming.

If the lines persist, spread, or are accompanied by other symptoms like nail thickening, it’s a good idea to see your doctor or dermatologist. With appropriate treatment when necessary, you can continue sporting your favorite dark nail polish looks.

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