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Nails that turn black or green

Discoloured nails may go unnoticed but they should be checked as they reflect one's health

Madam A went to her family doctor about a pinhead-sized black patch at the base of her big toenail.

She had noticed it for more than six months. The doctor thought it might be a fungal nail infection and prescribed a topical lotion.

But Madam A did not apply it regularly as she was too busy with her work at a retail shop.

The black nail did not cause any pain or discomfort. A year later, when she visited the clinic for a minor ailment, her doctor noticed that the black patch on the toenail had grown bigger.

She was promptly referred to a dermatologist, who arranged for a nail matrix biopsy. The test, which involves surgically removing a small sample of cells from the nail matrix, confirmed that Madam A had malignant melanoma, the most dangerous type of skin cancer. It is potentially fatal.

Melanonychia, or black nail, is a common condition showing brown to black discolouration of the nail, mostly due to benign causes.

Still, it is important to examine and investigate a band or line of pigmentation - known as longitudinal melanonychia - in a single nail as it may be a sign of melanoma.


Our fingernails and toenails are hard and translucent structures made up of keratin and are not normally pigmented. Pigmentation results from the deposition of melanin by pigment cells (melanocytes).

These typically lie dormant in the nail matrix where the nail originates. As the melanin is continuously deposited in the cells of the growing nail, a pigmented streak arises. This is called longitudinal melanonychia.

It typically starts as a single brown-black pigmented band or streak extending from the cuticle along the nail plate to its free edge, and may affect single or multiple nails. The pigmentation may go on to cover the entire nail.

Melanin deposits can be due to having more pigment cells, such as in people from ethnic groups with darker skin. Or it could be due to pregnancy, nail-biting, injury and friction, the side effects of certain medications and underlying chronic conditions.

It can also result from an increase in melanocytes due to a benign "mole" or lentigine in the nail matrix, or melanoma of the nail unit. The latter commonly affects the thumbs, index fingers and big toes.

Some types of bacteria, as well as fungal infection of the nail, can also produce melanin that discolours the nails.

Nicotine stains from cigarettes, certain medicated lotions and dirt can also stain our nails.

Injuries or ill-fitting shoes can cause bleeding under the nail, making it appear black.


Black lines or patches on nails very often go unnoticed because there are no symptoms. Or they may simply be dismissed as a minor cosmetic concern.

Some healthcare professionals may also not be aware of this problem. Many do not suspect that patients with blackened nails may be suffering from nail melanoma, thus leading to delayed diagnoses of such cases.

Having a black nail more commonly affects dark-skinned people and, less so, Caucasians.

It can start at any age, including childhood, and affects both males and females.

Cutaneous melanoma is the most common cause of death among skin cancer cases in Caucasians.

In comparison, melanoma is very uncommon in Asia, including Singapore. One may observe it simply as abnormal moles on the hands and feet, or black nails.

When detected early, nail melanoma can be treated.

If left alone, the cancer can spread and turn deadly. It is thus important to see a dermatologist early if there are any changes or discolouration in the nails.

Any new onset of longitudinal melanonychia in a single nail warrants a biopsy test to ensure that it is not linked to melanoma.

Our nails reflect our health. They are, in fact, much like a canvas on which life paints itself - offering important clues to our health and lifestyle habits, including underlying medical conditions.

Other than discoloured nails, one may spot abnormalities of the nail-plate surface and nail shape, cuticle and nail fold, or experience a loss of nails and skin growth affecting the nail area.

Unhealthy nails can also take on other colours. Yellow nails, for instance, can be due to psoriasis or a fungal infection.

If a person's nails look yellow, it may be a sign of lymphatic obstruction in cardiopulmonary disease, also known as the "yellow nail syndrome".

A pseudomonas bacterial infection can cause nails to turn green, while chronic kidney failure or liver disease may be reflected as certain patterns of white nails.

White streaks or spots may be caused by nail injury or even a manicure. They could also be due to certain fungal infections that affect the superficial nail plate.

Meanwhile, painful red patches or red lines on a person's nails could arise from tumours in the nail bed.

As for the colour blue, it could be linked to certain medications.

Fortunately for Madam A, the melanoma on her toenail was at an early stage and scans did not show that the cancer had spread elsewhere.

Her toe was successfully amputated and she was rid of the cancer.

•Dr Tay is a consultant dermatologist at Dermatology and Surgery Clinic. He specialises in skin cancer, dermatologic and nail surgery, aesthetic dermatology and laser procedures.

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A version of this article appeared in the print edition of The Straits Times on October 10, 2017, with the headline Nails that turn black or green. Subscribe