Melanonychia is a brown or black color in your nail. It can affect your fingernails or toenails. It can be in one nail, a few nails, or all of your nails. Melanonychia can have many different causes that range from harmless to potentially fatal. You should always have a doctor examine any dark streaks in your nails.
What Does Melanonychia Look Like?
Melanonychia can look differently depending on what caused it. It can appear as:
Longitudinal melanonychia or melanonychia striata. This type of linear melanonychia appears as brown, black, or gray bands that run from your nail bed to the tip of your nail.
Diffuse or total melanonychia. This involves your entire nail turning dark.
Transverse melanonychia. This type of melanonychia appears as a band that runs across your nail from one side to the other.
What Are the Types of Melanonychia?
Melanocytes are pigment cells that can release a brown-colored pigment called melanin. You have melanocytes in the nails of your fingers and toes. However, normally, the melanocytes are dormant. Since there is no melanin in your nails, they appear translucent. There are two ways that melanonychia occurs:
Melanocytic activation. This type of melanonychia occurs when the melanocytes are activated to produce melanin. The number of melanocytes stays the same.
Melanocytic proliferation. This type of melanonychia is a result of an increased number of melanocyte cells in the nails. The growth of melanocyte cells can be cancerous or noncancerous.
What Causes Melanonychia Due to Melanocytic Activation?
There are a number of causes of melanocytic activation. Some of these include:
Race. Melanonychia can naturally occur in African American, Hispanic, Indian, Japanese, and other dark-skinned races. It appears as multiple bands that go from the nail bed to the tip of the nail. It's more common in fingers and usually happens in multiple nails. The width of the bands may increase with age.
Pregnancy. Skin hyperpigmentation changes occur during pregnancy. Melanonychia can also be associated with pregnancy. It usually involves several fingernails and/or toenails. It may clear up after pregnancy or it may not.
Inflammation. Melanonychia can be caused by inflammatory skin diseases that affect your nails. It can also be caused by inflammation due to friction from shoes and biting your nails.
Tumors. Benign tumors and malignant tumors such as basal cell carcinoma can cause melanonychia.
Trauma. Acute and chronic trauma from injuries or repeated friction can cause melanonychia.
Systemic disease. This type of melanonychia is rare. It is usually present in multiple fingernails or toenails. When it does happen, it's usually associated with endocrine disorders such as Addison's disease, which is when your body doesn't produce enough of certain hormones.
What Causes Melanonychia Due to Melanocytic Proliferation?
Melanonychia due to melanocytic proliferation can be either benign, which means noncancerous, or cancerous. Benign causes of melanocytic proliferation include nevi, which are moles, and lentigo, which are flat, pigmented areas of skin.
Melanoma of the nail bed is the most serious possible cause of melanonychia. To diagnose melanoma under a nail, doctors use the ABCDEF criteria:
- A. Age in the 20 to 90-year range. Most common in people in their 50s to 70s. Most common in African American, Native American, and Asian races.
- B. Band of color that is brown-black, wider than 1/8th of an inch, border is irregular or blurred.
- C. Change in size or growth rate of band. May also refer to lack of change if the melanonychia has been treated.
- D. Digit involved, usually the thumb. One digit is more concerning than several. Melanoma is more common in the dominant hand.
- E. Extension of the color onto the surrounding tissues.
- F. Family or personal history of melanoma or unusual moles.
How Is Melanonychia Treated?
The treatment of melanonychia depends on the underlying cause. Benign causes don't necessarily need to be treated. Your doctor may just watch and see what happens. If it does need to be treated, some treatment options may include:
- Treating an underlying disease
- Stopping or changing medicine
- Avoiding trauma
- Treatment of infection
- Correcting nutritional deficiency
- Treatment for melanoma