An irregular black patch on the nail plate

Unless you know exactly what caused your toenail to turn black (like, you dropped a hammer on it last weekend), and it is not causing you much discomfort, it is best to have a doctor check out your black toenail to make sure nothing serious is going on.

Black Spots Under Toenail: 5 Causes of Black Toenails

Seeing your toenail turning black is alarming, and a range of issues can cause black spots under the toenail. Find out 5 potential causes in this article.

Seeing your toenail suddenly or slowly turning black is definitely alarming, but there are a range of issues that can cause black spots under toenail ranging from minor to more severe.

After reading this article, if you are still unsure what could be causing your black spots under toenail, or it is causing you significant distress, you should schedule an appointment with your doctor to get a full assessment of the situation.

Below are 5 things that can lead to your toenails turning black or having black spots.

1. Poor-Fitting Shoes

This one should be easy to identify.

If you wear shoes that are way too tight, or just fit in a strange way that causes your toenail to be constantly hitting the shoe or rubbing the nail constantly – it can damage the toe enough to cause blood to build up underneath giving the nail a black appearance.

Step one here is to get yourself to the shoe store to pick up a well-fitting pair of shoes.

2. Toe or Foot Injury

Any extreme injury to the toenail or foot may lead to blood vessels to break in the area and blood to pool underneath the nail.

Think back to if you really stubbed your toe, dropped something heavy on your foot, or have just been running a lot to train for that marathon, as all of these things may lead to a toe injury that causes your nails to turn black.

This type of nail injury may come along with a feeling of pressure under the nail, and in extreme cases, you may need to see a doctor to let them drill a tiny hole and let some of the blood out.

However, in the case of minor injury which is not causing you much pain, you may be able to treat a toenail injury at home with the RICE technique:

‍R – Rest the foot. This means to put your marathon training schedule on hold for a few weeks to allow the nail to heal.

‍I – Ice the toe to help reduce any inflammation and pain that you may be having. This can be done multiple times daily, but try not to ice for longer than 30 minutes at a time.

‍C – Compress the area to reduce inflammation using a bandage wrapped around the toe. This may help reduce the amount of blood that ends up pooling under the nail.

‍E – Elevate the affected foot to reduce swelling.

3. Melanoma

The most severe form of skin cancer, melanoma, can occur anywhere you have skin on your body, your toes included.

Melanoma usually appears as a dark brown to black unusually shaped spot, and when it occurs near or under the toenails it can look like a long dark streak through the nail. With melanoma, the surrounding toe skin may take on a darkened appearance as well.

If your black spots under toenail did not come from a direct injury or obvious nail fungus, you will need to see your doctor to ensure you are not dealing with something more serious like melanoma.

If you are diagnosed with melanoma, your doctor will go over the next potential treatment options for removal.

With melanoma, early detection is key! So, don’t brush off unusual dark spots under or around your toenails.

4. Toenail Fungus

A toenail fungus, also known as onychomycosis, is a common nail affliction that can usually be safely removed with prescription therapy over a long period of time.

While most nail fungi appear as yellow to brownish discolorations, sometimes the fungus can appear dark brown to black with the buildup of debris under the nail.

‍Yellow to brown to black nail discoloration

Brittle, crumbly, or ragged texture

Changes in nail shape

‍If all signs are pointing to a nail fungus, you can schedule an appointment with your local doctor for treatment, or have an Online Visit with our U.S. licensed doctors today.

Our Strut Nail Formula is a blend of multiple antifungal medications mixed into a base with a strong driving agent DMSO to make sure the ingredients get through the nail to the root of the fungus.

If you are a good candidate for treatment, your prescription nail fungus treatment can be shipped discreetly to your front door.

5. Certain Medical Conditions

Certain medical conditions have been found to cause one or many toenails turning dark or black.

‍These conditions may include:

‍Diabetes

You will need to speak with a doctor to make sure that the cause of your black toenails is one of these conditions and not something else like a fungus or melanoma.

If you have diabetes, you will need to see a doctor for anything happening involving your toes or feet, due to diabetics having increased risks of infection and generally worse wound healing.

In general, to help get rid of a black toenail caused by one of these conditions, the root condition would need to be improved.

When to see a doctor for black spots under toenails

Unless you know exactly what caused your toenail to turn black (like, you dropped a hammer on it last weekend), and it is not causing you much discomfort, it is best to have a doctor check out your black toenail to make sure nothing serious is going on.

A toenail fungus is a complicated fungal infection and often will need prescription antifungal medications to clear completely.

Bottom Line: If you don’t know why your nail turned black or you are having a lot of discomfort from the nail – go see a doctor for a diagnosis and treatment.

An irregular black patch on the nail plate

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

PMCID: PMC7509581 PMID: 33005709

History

A 57-year-old woman presented with a progressively enlarging irregular black patch of 1-year duration on the left fourth toenail (Fig 1). The patient denied new medications, history of trauma, or previous nail dyspigmentation. Proximal and lateral nail folds were not involved and pigmentation of the hyponychium was not evident. The patch could not be removed with scratching of the nail plate. Dermoscopy revealed nonlongitudinal, black to brown, reticular pigmentation with overlying white scale and distal onycholysis (Fig 2).

Fig 1.

Fig 2.

Question 1: What is the most likely diagnosis?

• A. Nevus of the nail matrix
• B. Fungal melanonychia
• C. Subungual melanoma
• D. Trauma-related nail plate hemorrhage
• E. Exogenous pigment

Answers:

• A. Nevus of the nail matrix—Incorrect. Nevi of the nail matrix are a common cause of longitudinal melanonychia in children and are characterized by uniform nests of cytologically banal melanocytes. Nevi tend to present with homogenous brown to black longitudinal bands. On dermoscopy, small dark granules less than 0.1 mm in diameter may be visualized and represent intracellular melanin inclusions.
• B. Fungal melanonychia—Correct. Fungal melanonychia is a rare nail infection caused by fungal organisms that produce melanin pigment, most commonly Trichophyton rubrum and Scytalidium dimidiatum.1 , 2 The dystrophic nail changes, onycholysis, subungual hyperkeratosis, and yellowish discoloration of the involved nail (and nearby nails) point to the clinical possibility of fungal infection. Additionally, the lack of trauma and the nonlongitudinal clinical appearance further support this diagnosis.
• C. Subungual melanoma—Incorrect. Subungual melanoma is an important cause of melanonychia, with concerning features that include presentation in the fifth to seventh decade of life, sudden onset or widening of irregular brown-black longitudinal bands, and pigment extension to the lateral or proximal nail fold (Hutchinson sign). 1 , 3
• D. Trauma-related nail plate hemorrhage—Incorrect. Nail plate hemorrhage is a common finding and often presents with red to maroon discoloration. Patients often report a history of trauma, anticoagulant use, or both. The diagnosis can be confirmed with nail plate clipping. 1 , 4
• E. Exogenous pigment—Incorrect. Exogenous pigment includes that from tobacco, dirt, potassium permanganate, tar, iodine, and silver nitrate. These substances may cause a brown to black pigmentation of the nails and can often be easily scratched off. These features are lacking in the presented case. 1

Question 2: What are key dermoscopic features of the correct diagnosis?

• A. Longitudinal brown to black lines with irregular color, spacing, and thickness, with pigment extension onto the hyponychium, revealing a parallel ridge pattern
• B. Gray homogenous band consisting of multiple thin homogeneous gray lines
• C. Red-black globules along proximal and lateral margins of homogenous pigment that lacks melanin granules
• D. Light- to dark-brown parallel striae that extend beneath a translucent eponychium
• E. White or yellow streaks, nonlongitudinal homogenous pattern, and reverse triangular pattern

Answers:

• A. Longitudinal brown to black lines with irregular color, spacing, and thickness, with pigment extension onto the hyponychium, revealing a parallel ridge pattern—Incorrect. Dermoscopic features suggestive of subungual melanoma may include irregular longitudinal brown to black lines with asymmetry in color, spacing, and thickness. Lines also may show parallelism disruption or blood spots.
• B. Gray homogenous band consisting of multiple thin homogeneous gray lines—Incorrect. This dermoscopic feature is a sign of benign melanocytic activation and may be observed in several diagnoses, such as drug-induced pigmentation or ethnic-type melanonychia. 1 , 4
• C. Red-black globules along proximal and lateral margins of homogenous pigment that lacks melanin granules—Incorrect. Homogenous red-maroon pigmentation with round globules at the periphery likely represents subungual hematoma. However, red-maroon pigmentation that does not resolve with nail growth may require additional histopathologic examination because of the concern for subungual melanoma. 4
• D. Light- to dark-brown parallel striae that extend beneath a translucent eponychium—Incorrect. This feature is known as pseudo-Hutchinson sign and is a common feature of nail matrix nevi, often observed in younger adults and children. 3 Other features of a nevus include the presence of melanin inclusion granules, regular nail band pattern, parallel lines, and uniform band thickness and spacing. 4
• E. White or yellow streaks, nonlongitudinal homogenous pattern, and reverse triangular pattern—Correct. These features, along with subungual hyperkeratosis, yellow or multicolor pigmentation, and white scale, are more significantly associated with fungal melanonychia than sources of melanocyte activation or melanocyte hyperplasia. 5 The presence of irregular reticular pigmentation has not previously been described, but may represent another dermoscopic feature of fungal melanonychia. Additional studies are needed to confirm the diagnostic accuracy of this feature.

Question 3: What is the best next step in confirming the diagnosis?

• A. Dermoscopic short-term monitoring alone
• B. Nail matrix biopsy
• C. Nail clipping
• D. Reassurance
• E. Amputation

Answers:

• A. Dermoscopic short-term monitoring alone—Incorrect. Although monitoring for pigment clearance is important, short-term monitoring with dermoscopy does not confirm the diagnosis of fungal melanonychia. Pigmented onychomycosis requires antifungal treatment to assist with infection clearance, allowing pigment to clear as the nail grows out. 2
• B. Nail matrix biopsy—Incorrect. If clinical or dermoscopic features were concerning for subungual melanoma, a nail matrix biopsy would be recommended as the best next step. Given the lack of melanoma-specific clinical or dermoscopic features, alternative diagnostic evaluation should be performed first. However, a nail matrix biopsy may be considered for cases refractory to antifungal treatment to rule out subungual melanoma. 2
• C. Nail clipping—Correct. Nail clipping is the best next step to confirm onychomycosis. Nail clipping in this patient case demonstrated a dystrophic nail plate with subungual parakeratosis and neutrophil collections. Fontana-Masson stain and periodic acid–Schiff stain with diastase revealed numerous fungal organisms that contained melanin, preferentially located on the nail plate surface. However, pigment associated with fungus is often best observed on hematoxylin-eosin staining of a nail clipping.
• D. Reassurance—Incorrect. Reassurance alone without follow-up or treatment would not be appropriate for this patient. Additionally, surveillance for pigment clearance is important to ensure that the nail pigmentation is not associated with an underlying malignancy.
• E. Amputation—Incorrect. Amputation of the involved digit may be considered for the treatment of locally advanced melanoma. Amputation is not recommended for onychomycosis, the diagnosis presented in this patient case. 4

Footnotes

Funding sources: None.

Conflicts of interest: None disclosed.

References

• 1. Piraccini B.M., Dika E., Fanti P.A. Tips for diagnosis and treatment of nail pigmentation with practical algorithm. Dermatol Clin. 2015;33(2):185–195. doi: 10.1016/j.det.2014.12.002. [DOI] [PubMed] [Google Scholar]
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• 5. Ohn J., Choe Y.S., Park J., Mun J.-H. Dermoscopic patterns of fungal melanonychia: a comparative study with other causes of melanonychia. J Am Acad Dermatol. 2017;76(3):488–493.e2. doi: 10.1016/j.jaad.2016.08.013. [DOI] [PubMed] [Google Scholar]

Articles from JAAD Case Reports are provided here courtesy of Elsevier

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