A dark discoloration affecting part of a toenail often prompts concern. This change in nail appearance can stem from a variety of sources, ranging from minor, everyday occurrences to indications of more significant underlying health concerns. Understanding the potential origins of such discoloration can help in determining appropriate next steps.
Common Reasons for Dark Toenail Discoloration
A subungual hematoma is a frequent cause of dark toenail discoloration. This condition results from trauma, such as stubbing a toe or dropping a heavy object on the foot, which causes small blood vessels under the nail plate to rupture. The trapped blood then pools beneath the nail, creating a dark discoloration that resembles a bruise and typically resolves as the nail grows out over several months.
Fungal infections, medically known as onychomycosis, are another common reason for toenail discoloration. These infections occur when fungi penetrate the nail plate, often through small cracks or separations. The fungi can cause the nail to thicken, become brittle, and develop a yellow, brown, or even black hue. They can spread and may require antifungal treatments.
Repeated pressure or friction from ill-fitting shoes or prolonged physical activity can cause toenail darkening. Shoes that are too tight can repeatedly press against the nail, leading to micro-trauma and blood clots or pigment changes beneath the nail. Activities like running or hiking with inadequate footwear can also cause these changes.
Dark nail polish can stain the nail plate, leaving temporary discoloration. This staining is superficial and affects the surface layers of the nail. The discoloration fades as the stained outer layers of the nail wear away or grow out.
Underlying Medical Conditions
A serious cause of a dark toenail is subungual melanoma, a type of skin cancer that develops under the nail. It often appears as a dark streak that runs vertically from the cuticle to the tip of the nail. Unlike a bruise from trauma, this streak may widen over time, involve the nail fold, or exhibit irregular borders and color variations, signifying aggressive growth.
Certain systemic diseases can cause nail discoloration. For example, chronic kidney disease can lead to “half-and-half nails,” where the half of the nail closest to the cuticle appears white, and the half closer to the tip appears reddish-brown or dark. Psoriasis, an autoimmune condition, can also affect the nails, causing discoloration, pitting, and separation from the nail bed.
Circulatory problems, such as peripheral artery disease, can impair blood flow to the extremities, including the toes. Reduced oxygen and nutrient supply to the nail bed can lead to nail discoloration, along with other symptoms like pain or numbness in the feet. These conditions reflect broader health issues and require medical evaluation.
Some medications, including certain antibiotics, antimalarial drugs, and chemotherapy agents, can induce nail discoloration as a side effect. The specific hue and pattern of discoloration can vary widely depending on the medication. This type of discoloration resolves after the medication is discontinued, though it may take time for the nail to grow out.
When to See a Doctor
Seek medical attention if a dark toenail discoloration appears without a clear cause, such as a known injury. Any persistent or worsening dark streak under the nail that does not seem to grow out with the nail’s natural progression requires evaluation. This is important if the discoloration changes in size, shape, or color over time.
Consult a healthcare provider if the dark area is accompanied by pain, swelling, or pus around the nail, as these indicate an infection or inflammatory process. Changes in the nail’s texture, such as thickening, crumbling, or lifting from the nail bed, alongside discoloration, also suggest medical assessment.
A dark streak that extends from the nail plate into the cuticle or the surrounding skin, a phenomenon known as Hutchinson’s sign, requires immediate medical review. This specific sign can indicate subungual melanoma. If multiple nails become discolored without a clear reason, or if there is a personal or family history of melanoma, medical consultation is advised.
Prevention and Nail Care
Maintaining proper foot hygiene supports toenail health and can prevent discoloration. Regularly cleaning and thoroughly drying the feet, especially after bathing or swimming, deters fungal growth. Allowing feet to air out and avoiding prolonged exposure to damp environments reduces the risk of infections.
Wearing well-fitting shoes prevents trauma and pressure-related discoloration. Shoes that are too tight or too loose can cause repetitive micro-trauma to the nails during walking or running. Opting for breathable materials helps manage moisture around the feet, contributing to a healthier nail environment.
Trimming toenails straight across and avoiding cutting them too short prevents ingrown nails and reduces injury to the nail bed. Using clean, sharp nail clippers ensures a smooth cut, minimizing splintering or jagged edges that invite fungal entry. Regular self-inspection of the nails allows for early detection of any unusual changes, enabling timely intervention.