Why do you have dark toenails? Discover the possible causes and treatment options for this common medical problem.

Do you ask why the foot nail is dark? Discover the possible causes and treatment options for this common medical problem.

If you have noticed that your toenail has darkened, it could be a sign of an underlying medical condition. One possible explanation for a dark nail is a condition called subungual hematoma. This occurs when there is bleeding under the nail, leading to dark discoloration. Subungual hematomas usually occur as a result of trauma or injury to the finger, such as a blow or the fall of something heavy.

The dark color of a toenail can also be indicative of a fungal infection. Fungal infections, such as onychomycosis, thrive in warm, humid environments and can cause nail discoloration. In the case of toenail fungus, the affected nail may appear yellow, brown, or black, as well as thicken and become brittle.

Subungual hematoma: Condition characterized by bleeding under the nail, causing dark discoloration. It is usually caused by trauma or injury to the toe.

Toenail fungus (onychomycosis): Fungal infection that causes discoloration, thickening, and brittleness of the toenail.

Why is my toenail turning dark?

Fungal infection: One of the most common causes of darkening toenails is fungal infection. Fungus thrives in warm, humid environments, making toenails susceptible to infection, especially if proper hygiene is not maintained. A fungal infection can cause discoloration, thickening, and brittleness of the nail. It is important to see a doctor and receive treatment to prevent the infection from spreading to other nails.

Common Causes of Dark Toenails

Injuries or trauma: A common cause of dark nails is an injury or trauma to the nail bed. This can be caused by accidental trauma, such as dropping a heavy object on the finger, or repetitive actions, such as playing sports, that put pressure on the nails. When the nail bed is traumatized, bleeding can occur under the nail, resulting in dark discoloration.

It is important to note that if toenail discoloration is a result of injury or trauma, it will usually disappear as the nail grows. However, if the darkening persists or spreads, it is advisable to seek medical attention to rule out other possible causes.

Fungal infections: Fungal infections can also cause darkening of toenails. Fungus thrives in warm, humid environments, making feet and nails vulnerable. When a fungal infection develops, it can cause discoloration of your toenails, turning them dark, yellow, brown, or even black. This is usually accompanied by other symptoms, such as thickening, fragility, and an unpleasant odor.

If you suspect you have a fungal infection, it is important that you seek appropriate medical treatment as soon as possible. If left untreated, fungal infections can spread and lead to complications and potential damage to the nails and surrounding skin.

Other possible causes: In addition, there are other factors that can contribute to the appearance of dark nails. These include certain medications, underlying medical conditions such as diabetes or circulatory problems, and even wearing tight shoes or constantly applying nail polish without letting your nails breathe. In some cases, it may be necessary to consult a healthcare professional to determine the exact cause of the discoloration and receive appropriate guidance.


  1. Injuries or trauma to the nail bed can cause darkening of the toenails.
  2. Fungal infections are a common cause of dark nails with accompanying symptoms.
  3. Other possible causes are medications, underlying diseases and certain lifestyle habits.

Fungal Infections and Dark Toenails

Types of fungal infections:

  1. Distal Subungual Onychomycosis: This is the most common type of fungal infection that affects the toenails. It typically begins at the edge of the nail and progresses toward the base of the nail, causing discoloration and thickening.
  2. Superficial onychomycosis: This type of infection usually affects the surface of the nail, causing white or yellow spots and making the nail appear scaly or powdery.
  3. Proximal subungual onychomycosis: This less common form of fungal infection usually begins at the base of the nail and progresses toward the tip. It is often associated with disorders of the immune system.

It is important to note that not all darkened toenails are caused by fungal infections. Other possible causes are trauma, psoriasis, melanoma, and certain medications. It is essential to consult a healthcare professional to obtain an accurate diagnosis and appropriate treatment.

When treating fungal infections, there are several options, such as topical antimicotic medications, oral antimicotics and, in severe cases, surgical removal of the affected nail. It is important to seek professional advice to determine the most appropriate treatment plan based on gravity and type of infection.

Signs of fungal infection Prevention tips
  • Discoloration (yellow, brown or black)
  • Thickened or brittle nails
  • Bad smell
  • Pain or discomfort
  • Keep your feet clean and dry
  • Use Breathable Footwear and Socks
  • Avoid sharing personal objects such as clippers or shoes
  • Avoid walking barefoot in public places

Injuries and Trauma Leading to Dark Toenails

Injuries: A sudden blow or strength in the finger nail can cause the breakage of the blood vessels located under the nail bed. This causes blood accumulation, which is often manifested with a dark or black color. Some common examples of injuries are hitting their finger against a hard surface, dropping a heavy object on the foot or suffering a spor t-related injury.

“The lesions that cause dark nails usually give rise to subungual bruises, which are blood clots trapped under the nail sheet. These bruises can cause important pain and discomfort and, if they are not treated, they can cause complications such as an infection.”

Trauma: Continuous pressure or repetitive trauma can also contribute to the darkening of feet nails. People who frequently carry out activities that excess excessive pressure on feet nails, such as running long distances or practicing hig h-impact sports, are more likely to suffer this condition. In addition, inappropriate footwear that excessive pressure on feet can also contribute to trauma and consequent discoloration.

  1. Long distance races or hig h-impact sports practice can cause microtrauma in feet nails and darken them over time.
  2. Inappropriate footwear can exert chronic pressure on the fingernails, which causes dark discoloration and possible injuries.

In summary, injuries and trauma are important factors that contribute to darkening feet nails. Whether it is a sudden blow to the finger and continuous pressure, understanding and recognizing the causes of discoloration of feet nails is crucial to determine the proper treatment and preventive measures.

Melanoma and Dark Toenails

Melanoma signs on the fingernails:

  • Darkening of the nail bed, typically brown or black.
  • Irregular or asymmetric discoloration.
  • Enlargement of the affected nail.
  • Changes in the form or texture of the nail.
  • Development of a vertical or horizontal stripe or band of color on the nail.

Melanoma can develop on any nail, but is most common on the big toe or thumb. It is important to note that not all darkened toenails are necessarily melanomas, as other factors such as trauma, fungal infections, or medications can also cause discoloration. However, if you notice any unusual changes in your toenails, it is essential that you consult a healthcare professional for a proper diagnosis and appropriate medical advice.

Melanoma risk factors:

  1. Personal or family history of melanoma.
  2. Prolonged exposure to ultraviolet (UV) radiation, either from the sun or tanning beds.
  3. Light skin, light hair and light eye color.
  4. A large number of moles on the body.
  5. Have a weakened immune system.

Other medical conditions associated with dark toenails

1. Subungual hematoma: Often caused by a traumatic injury to the toe, a subungual hematoma refers to the collection of blood under the nail plate. This can lead to dark discoloration of the toenail, ranging from deep red to black. Blood trapped under the nail can cause pressure and discomfort.

  • It occurs due to direct injuries or repetitive trauma to the toe.
  • The discoloration appears gradually and may be associated with pain.
  • Treatment involves relieving pressure by draining the hematoma or, in severe cases, removing part of the nail.

Note: It is important to seek medical attention for a subungual hematoma, as it can mimic other conditions such as melanoma, a type of skin cancer.

2. Melanonychia: This condition refers to dark pigmentation of the nail plate, which can present in several ways:

  1. Longitudinal melanonychia: presence of dark lines parallel to the length of the nail. These lines may be benign or indicate a more serious underlying condition.
  2. Transverse melanonychia: It is characterized by the presence of dark bands that extend horizontally across the nail. It can be caused by systemic medications or certain diseases.
  3. Diffuse melanonychia: Uniform darkening of the entire nail, usually caused by medications or systemic disorders.

It is crucial to differentiate between benign pigmentation and potentially malignant melanoma, which requires proper evaluation by a healthcare professional.

Causes of melanonychia Associated conditions
birthmarks Psoriasis
Medications (such as certain antibiotics, antimalarials) lichen planus
Idiopathic (unknown cause) Renal insufficiency

When to seek medical attention for dark toenails

  1. If foot nail decolor is accompanied by pain, swelling or bleeding, it can be an indication of an injury or infection that requires medical examination. These symptoms can be the result of a trauma, such as a blow to the finger or the fall of something heavy, which causes a subungual hematoma or a fungal infection on the nails.
  2. People who notice a sudden and significant change in the color of the nails of the feet, especially if it is accompanied by other worrying symptoms such as bad smell or secretion, should seek medical attention. This could be a sign of an underlying medical condition, such as melanoma, a type of skin cancer that can appear as a dark spot under the nail.

It is essential not to ignore the persistent darkening of the feet nails or any related symptoms, since a medical intervention in time can avoid greater complications and guarantee adequate treatment.

It should be noted that changes in feet nail color may also be influenced by lifestyl e-related factors or external causes. For example, repetitive trauma caused by inappropriate footwear or by rigorous physical activities can cause a “finger of the corridor”, which causes the darkening and the appearance of bruises on the fingernails. In addition, some underlying medications or health problems, such as ferropenic anemia, can contribute to nail discoloration. However, given any questions or concern, it is always better to consult a healthcare professional to perform an appropriate evaluation and diagnosis.

Author of the article
Dr.Greenblatt M.
Dr.Greenblatt M.
Medical oncologist at the Robert Larner College of Medicine, MD, at the University of Vermont

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