It can be unsettling to observe a change in the color of a toenail, especially when it begins to darken. While a dark toenail might cause concern, various factors, from minor injuries to serious underlying conditions, can contribute to this discoloration. Understanding these potential causes can help individuals determine the appropriate next steps.
Physical Causes and Injury
One common reason for toenail darkening stems from physical trauma. An impact to the toe, such as dropping a heavy object on it or stubbing it forcefully, can rupture small blood vessels beneath the nail plate. This leads to bleeding that forms a subungual hematoma. The trapped blood appears dark, often black, purple, or deep red, similar to a bruise elsewhere on the body.
Repetitive friction or pressure from ill-fitting footwear can also cause this type of trauma. Shoes that are too tight, too loose, or lack adequate support can lead to the toes repeatedly hitting the front or sides of the shoe. This constant micro-trauma can result in small, recurrent bleeding episodes under the nail, gradually leading to darkening over time. The discoloration typically grows out with the nail as the injured area heals.
Some individuals may also notice dark lines or patches on their toenails due to natural pigmentation. This condition, known as benign melanonychia, occurs when pigment-producing cells in the nail matrix create melanin, which is incorporated into the nail plate. It is more common in individuals with darker skin tones and usually appears as a brown or black streak running from the cuticle to the tip of the nail. This is generally a harmless variation of normal nail growth.
Infections Affecting Toenails
Infections are another frequent cause of toenail discoloration. Fungal infections, medically termed onychomycosis, are particularly common culprits. Fungi can invade the nail plate, causing it to thicken, become brittle, and change color. The discoloration often appears yellow, brown, or even black, and this dark appearance can be exacerbated by debris accumulating under the infected nail.
The fungi thrive in warm, moist environments, making toenails particularly susceptible, especially for those who frequently wear closed-toe shoes or are in public wet areas. As the infection progresses, the nail may lift from the nail bed, potentially leading to discomfort. The discoloration often results directly from the fungal organisms or their byproducts within the nail structure.
While less common than fungal infections, certain bacterial infections can also cause toenail discoloration. For instance, Pseudomonas aeruginosa bacteria can lead to a greenish-black discoloration of the nail. This typically occurs when bacteria become trapped between the nail plate and the nail bed. The pigment produced by the bacteria results in the distinct green or black hue.
Systemic Issues and Medications
Darkening toenails can sometimes signal more widespread health concerns or be a side effect of certain medications. A serious concern, though rare, is subungual melanoma, a form of skin cancer that originates in the nail matrix. This condition often presents as a dark brown or black streak that typically extends from the nail bed to the tip of the nail, and may involve the skin around the nail (the cuticle or nail fold). Unlike a bruise, which grows out with the nail, a melanoma streak may persist, widen, or change in color over time, and it generally does not shift with nail growth.
Certain systemic diseases can also manifest with nail changes, including discoloration. Conditions such as chronic kidney disease, heart conditions, or diabetes can sometimes lead to altered nail appearance. These changes are often subtle and may include variations in nail texture, shape, or color, reflecting the body’s overall health status. While not always directly causing dark discoloration, these conditions can sometimes lead to other nail issues.
Several medications can also induce nail pigmentation as a side effect. Some antibiotics, certain anti-malarial drugs, and various chemotherapy agents are known to cause nail discoloration. The darkening can range from diffuse brownish patches to distinct dark lines, and the specific appearance often depends on the type and dosage of the medication. This discoloration usually resolves after the medication is discontinued, though it may take time for the affected nail to grow out completely.
Knowing When to Seek Professional Advice
Seek professional medical advice if toenail darkening causes concern or is accompanied by other symptoms. If a dark spot or streak on the toenail does not appear to grow out with the nail over several months, or if it seems to be spreading, a healthcare provider should evaluate it. This persistence suggests the discoloration is not simply a bruise resolving naturally.
Consulting a medical professional is also advisable if the darkened toenail is accompanied by pain, swelling, redness, or an unpleasant odor. These symptoms often indicate an underlying infection or inflammation that requires treatment. Also, if the cause of the darkening is uncertain and did not result from an obvious injury, a medical evaluation can help identify the root problem.
Particular attention should be paid to any new dark streak, especially if it extends to the cuticle or nail fold, or if there is a personal or family history of skin cancer. A healthcare provider can properly differentiate between benign conditions and more serious concerns like subungual melanoma. For individuals with existing chronic health conditions, discussing any nail changes with their doctor is also important, as these changes could sometimes be linked to their overall health.