If you have noticed that one or several toenails have turned a black color, it is only normal to ask yourself about the cause behind the problem. While in the majority of the situation the main culprit is a fungal infection, there are other causes that can lead to similar changes.
Getting a correct diagnosis is essential, especially since a black toenail can also represent a sign of cancer (malignant melanoma). The sooner an adequate diagnosis is made, the sooner the right treatment can be started.
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Chromonychia, a term that includes all nail color changes
According to the Text Atlas of Nail Disorders, chromonychia is a term generally used to describe all changes that occur at the level of a nail, in terms of color. The affectation can refer to both the surface of the nail and the subungual tissues. There are a number of factors to be taken here into consideration, such as the previous transparency of the nail, as well as its state of health and the one of underlying tissues.
It is important to understand that there are a number of causes that can lead to the excess accumulation of pigment at the level of the nail, including the excessive production of melanin.
The accumulation of hemosiderin, copper or various drugs can modify the color of the toenails as well. If the skin vessels are affected or the person suffers from underlying conditions, such as anemia, it is possible that the color of the nails is going to change as well. The same goes for those who have suffered from carbon monoxide poisoning.
Upon visiting the dermatologist, he/she will examine the aspect of the toenails, in order to determine the exact cause behind color changes. During the examination process, it is important to keep the toes relaxed and not pressed hard against the floor (this will influence the color of the nail bed).
Melanonychia or when your nails turn a black/brown color
Melanonychia is a term used to describe nails that have turned either a black or a brown color. As the authors of the Text Atlas of Nail Disorders  point out, it is important to take such changes into consideration, as one of the potential causes is actually malignant melanoma.
What are the other causes of black toenails? The list includes exposure to silver nitrate, injury/trauma resulting in hemorrhage, fungal infections, naevi, race or taking certain drugs, such as doxorubicin or cyclophosphamide.
A particular form is longitudinal melanonychia, a condition which is characterized by a longitudinal black line on the surface of the nail. This change can be idiopathic but it is also present in dark-skinned individuals, without being a pathologic sign.
People who suffer from various underlying conditions can present such characteristic changes: Addison’s disease, Cushing’s disease (followed by removal of adrenal glands), cancer (breast), drugs, exposure to radiation, digestive disorders (malnutrition), treatment against cancer (chemotherapy).
Pregnant women, those who have been diagnosed with secondary syphilis or those who present vitamin B12 deficiency can also present longitudinal melanonychia.
A number of dermatological conditions can lead to such changes, including primary amyloid, basal cell carcinoma and toenail bacterial infections. Lichen planus, Bowen’s disease, porphyria and radiodermatitis are also on that list. Radiotherapy, as a form of treatment, can lead to melanonychia, especially when performed on a long-term basis. Melanonychia is also encountered in those who have suffered frequent injuries or acute trauma.
Longitudinal melanonychia is a condition that can be present in children as well. According to a study published on the US National Library of Medicine, such changes are present in children, being either caused by lentigo or nevus. The study in question regarded children under the age of 16 and it confirmed that such changes are always benign (no cases of malignant melanoma identified).
Another study, published as well on the US National Library of Medicine, discussed about longitudinal melanoma as being caused either by melanocyte activation (excess production of melanin) or proliferation (as it happens in patients diagnosed with malignant melanoma, nevus or lentigo). The authors of the study highlighted the fact that matrix biopsy is essential for the confirmation of the diagnosis (especially when malignant biopsy is concerned).
The correct diagnosis is more important than you might think
Yes, your black toenail could be caused by a fungal infection. But, at the same time, you could suffer from malignant melanoma (one of the most dangerous forms of cancer). The doctor can make a correct diagnosis by performing a thorough medical examination, taking your medical history (other family members diagnosed with cancer) and performing a biopsy (if the suspicion of cancer is valid).
There are a number of signs that can point out in the direction of a fungal infection. For example, the affected toenail is brittle, thickened and discolored. The skin around it is scaly and a foul odor comes from the respective area. Purulent discharge can appear and, in more severe cases, the nail can become loose (and even completely detached).
Discolored nails are almost always a sign of fungal infections, especially if they are accompanied by the above-mentioned symptoms. Left untreated, the fungus will spread, attacking not only the nail but also the nail bed. The discoloration will only progress, until the nail turns a darker shade (black).
As you might be aware of, injuries leave the toenails exposed, increasing the risk of fungal infections. One practically enters into a vicious circle – the fungal infection affects the health of the toenails, leaving them prone to injuries, which further reinforce the power of the fungus. Fungal infections are treated with topical creams & medicated nail polishes, oral medication (Lamisil) and laser therapy. Removal is recommended in severe cases, being followed the antifungal treatment of the nail bed.
Malignant melanoma, on the other hand, presents a different symptomatology. In the majority of the cases, only one digit is affected and the pigmentation spreads to the periungual area. Moreover, the initial band continues to darken, as the condition progresses (with the borders becoming blurred with the passing of time). The correct diagnosis is more important than you might think; misdiagnosis can delay the adequate treatment, given the tumor time to spread and reach a life-threatening stage.
Patients who suffer from malignant melanoma can either present black stripes or spots on their toenails. The blurred borders are not a positive sign, suggesting that the condition has advanced. The same goes for the longitudinal line that becomes thicker, wider and darker in color.
Unfortunately, in a lot of cases, the cancer begins in the nail matrix, taking a lot of time before it is correctly diagnosed (in most situations, the discoloration is attributed to a fungal infection). The family history of cancer can guide the doctor in the right direction.
According to a study published in the Brazilian Dermatological Journal, the dermatoscopic examination of the nail matrix and bed is essential for an accurate and early diagnosis. It is highlighted that such examinations can allow for cases of malignant melanoma to be diagnosed as early as it is possible, thus guaranteeing the best prognosis for the patient in question. Once the diagnosis has been made, the patient will have to undergo chemotherapy or radiotherapy. The amputation of the affected toe can guarantee the best prognosis, as it will ensure that the cancer will not spread further.
Other causes of black toenails
If the toenails have a greenish-black discoloration, this is a sign that the patient in question might suffer from an infection with pseudomonas aeruginosa. These infections are difficult to treat, due to the high resistance to treatments.
It has been briefly mentioned that trauma or injuries can cause the toenails to become black. This is quite true, the appearance of the affected toenail being caused by the damaged blood vessels. As the blood collects under the nail bed, it will cause the toenail to appear red, blue or even purple. As the nail begins to heal and the blood to be resorbed, it is possible that the nail will turn black. It may also be painful and detached from the nail bed (partially/totally).
The most common situation is the one in which a heavy object is dropped on a person’s foot. The pain is most intense immediately after the injury, being accompanied by a pulsating sensation. However, it is important to understand that repetitive trauma can lead to such problems. For example, if a person wears shoes that are too tight, the constant pressure can damage blood vessels, causing one’s toenails to turn black. Similar problems are encountered in professional athletes, due to the fact that the forefoot constantly hits the shoe.
Keep in mind that injured toenails present a high risk for fungal infections, so it is important to keep them dry and clean. You might also want to use antifungal powder, for preventative purposes. In the situation that an injury has occurred at the level of the toenails, there are not many things that you can do, as such injuries often heal by themselves. Maintaining excellent foot hygiene will stimulate a faster and more efficient healing process.
If you experience intense pain, as well as a sensation of pressure or bleeding at the level of the nail, the doctor might decide to remove the affected nail and treat the nail bed against infection. As an alternative to the removal, he/she might drill a small hole in the toenail, in order to provide the blood with an exit point and reduce the pain & pressure experienced.
Verdict: is my black toenail caused by fungus?
Yes, your black toenail can be caused by a fungal infection. If you suspect that such a problem has occurred, it is time to visit your dermatologist and get a correct diagnosis. As you have seen, there are other conditions that can modify the color of your toenails, so you should seek out a specialist to be certain of the underlying problem.
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 A Text Atlas of Nail Disorders, Martin Dunitz, 2003. Retrieved from: http://www.rusmedserv.com/mycology/html/Atlas_of_Nail_Disorders.pdf
 Longitudinal melanonychia in children: a clinical and histopathological study of 40 cases. US National Library of Medicine. 1999. Retrieved from: http://www.ncbi.nlm.nih.gov/pubmed/10411404
 Tangential biopsy thickness versus lesion depth in longitudinal melanonychia: a pilot study. US National Library of Medicine. 2012. Retrieved from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3312251/
 Melanonychia: the importance of dermatoscopic examination and of nail matrix/bed observation. 2009. Brazilian Dermatological Journal, vol.84, no.2. Retrieved from: http://www.scielo.br/scielo.php?pid=S0365-05962009000200013&script=sci_arttext&tlng=en