Dark-colored stripes on the toenails are common in the United States, especially among people with darker skin on their toes, particularly African-Americans. For the most part, these streaks usually represent non-serious conditions. However, especially in fair-skinned people, the presence of these stretch marks could represent a deadly cancer. This article will discuss the common causes or dark streaks on toenails, and what condition is cause for alarm.

Before beginning, the reader should be aware while reading this article that the information contained is not intended to provide personalized medical advice specific to one’s medical condition, but rather is intended as a general discussion of this health topic. Any specific questions or concerns about the conditions described in this article should be directed to your own general practitioner or specialist for proper diagnosis and treatment.

The toenail is a dense tissue made of compressed keratin. The nail plate itself begins at the nail matrix, which is essentially the root of the nail. The outer edge of the matrix is ​​seen externally as the lunula, or the white semicircular area at the base of the nail just beyond the cuticle. The nail slowly grows outwards, sliding semi-loosely along the skin. The color of the nail itself is kind of off white or cream, with some clarity to see the skin under it. Discolorations on the nail plate, whether solid white, yellow, blue, brown, or black, are abnormal and represent a disease process. The most common sources of toenail discoloration are due to keratin debris built up under the nail due to natural thickening and aging of the nails, as well as discoloration from a fungal infection. They typically create a white, yellow, or yellowish-brown discoloration. Since both of these extensive topics have been covered by this author in other articles, the causes of darker shades of discoloration will be presented here.

Dark toenail discoloration has several causes, and correctly diagnosing the cause is key to successful treatment. The most common reason nails turn dark is from a bruise under the nail. Bruises are essentially blood left behind by bleeding. It can occur under the skin and can also occur under and on top of the skin located directly below the toenail. Bleeding under a toenail can be caused by a heavy object falling on the toe, pressure from tight shoes, toes getting stuck in the toe of the shoe as is often seen in runners, and from stroke injuries that cause blood vessels to rupture. Spontaneous rarely occurs, and often if one doesn’t remember injuring their toe, it usually means the injury was mild enough not to cause memorable initial pain. The bruise under the nail remains on the nail plate until it grows out along with the nail.

Bruising that does not grow as the nail continues to grow is cause for concern and a podiatrist should be contacted. The possible cause of this will be discussed later. When the bruise occupies less than a quarter to a third of the nail, it is likely to be left alone and the nail allowed to grow. If the hematoma is more extensive and covers the entire nail area, the nail plate should be removed. This is done for two reasons. First, it allows the blood to drain properly and limits the amount of damage the bleed caused to the root of the nail when it slightly lifted the nail plate during the active bleed time. Second, the bleeding may have been caused by a deep cut in the skin under the nail plate during the initial injury, and this skin should be evaluated for any cuts that need to be sutured. Another concern, especially if there has been a fracture in the bone under the nail, is bone fragments sticking out of the skin externally. If they are not removed and the skin is properly cleaned and treated, an infection can develop which can spread to the underlying bone.

Another cause of dark discoloration is infection. As discussed above, fungus can enter the skin under the nail and cause discoloration, thickening, brittleness, and debris. This fungus belongs to the same group of organisms that causes athlete’s foot and color-wise it can change the nail from dull to solid white, yellow, grey, brown or even black in some cases. Treatment is somewhat complex, as only certain medications have scientifically proven efficacy, and many home treatments are still used that simply do not show any real value. Another source of infection is bacteria, specifically bacteria from a family of organisms called Pseudomonas. This bacterium is prone to invading skin that has been kept moist for a while, and is commonly spread in hot tubs and hot tubs. The bacterium creates a green color change in skin and nail tissue, presumably from iron pigment. The so-called green nail syndrome is common and is treated with a special solution of diluted vinegar (acetic acid) or with specific antibiotics directed against pseudomonas. This infection rarely progresses to a more serious condition in healthy people and is usually easily treated.

Nail discoloration that moves across the width of the nail in a thin line from one side to the other has many different causes to discuss in detail. Causes can include kidney disorders, deficiencies of certain minerals, toxic metal poisoning, heart disease, cancer chemotherapy, certain chronic medications, and major injuries to the body. Due to the wide variety of causes, a visit to your primary care physician, dermatologist, or podiatrist is recommended. There is usually no immediate treatment for these lines, but one’s doctor can diagnose another condition that needs treatment by examining the nail, especially if something like metal poisoning or mineral deficiency is not diagnosed.

Nail discoloration that travels in a streak from the beginning to the end of the nail is the most concerning symptom. This stripe is usually brown, dark blue, or black and can be found on one side of the nail or in the center. Usually this stripe is less than a quarter of the width of the nail itself, although in some cases it can be wider. The usual cause of this streak is the overproduction of the cells that produce skin pigmentation, also called melanocytes. These cells produce melanin, which gives darker-skinned people their skin tone and Caucasians their tan. It naturally protects the skin from the sun’s harmful ultraviolet rays, although overexposure to the sun can cause a mutation in melanocyte production. This is technically a cancerous growth. In most cases of nail stains and skin conditions such as moles, it is a benign growth. However, a malignant cancer can develop that has the potential to spread to other organs and cause death. This cancer is called melanoma and it is deadly. Dark streaks that start at the cuticle and travel the length of the nail are very common in people with darker skin tones, particularly African-Americans.

In fact, many people have stripes on almost all of their toenails and have had them since birth. These do not usually represent nail melanoma and are usually benign. When these stripes develop recently in Caucasians, or if there is a new growth or change in a pre-existing stripe in someone with darker skin, the nail and surrounding skin should be evaluated by a doctor. This is especially true if skin discoloration is developing next to the nail, regardless of the original skin tone. A biopsy of the scratched part of the nail, the root of the nail, and the surrounding area of ​​skin should be done to make sure there is no malignant cancer. This is a simple procedure, usually done in an office by a podiatrist, dermatologist, or sometimes a general surgeon or family doctor, and it heals quickly. The nail usually grows back healthy if the condition was benign. If melanoma is present, immediate attention should be paid to the toe to prevent further spread. This usually includes amputation of the tip of the toe or the entire toe, depending on the size of the melanoma. This is absolutely necessary to save life and prevent the spread of cancer.

As you can see, dark toenail discoloration can have numerous different causes. Most are benign and resolve with simple treatment. Some are simply genetic, like the common streaks on the nails of darker-skinned people. Others are dangerous cancers that need immediate treatment. Due to the potential for cancer, this author recommends that all areas of dark nail discoloration be evaluated by a physician to ensure the condition is benign. The least you waste is a little time in the doctor’s office, and at best you may save your own life.