A dark toenail can be a surprising and sometimes unsettling discovery. While often a benign occurrence, a change in toenail color can also indicate underlying issues that warrant attention. Understanding the various reasons why a toenail might darken is a first step toward addressing the concern.
Blood Under the Nail
A subungual hematoma, essentially a bruise under the nail, is a frequent reason for a dark toenail. Trauma, like stubbing a toe or dropping a heavy object, can rupture small blood vessels beneath the nail, causing blood to pool and leading to discoloration from red or purple to dark brown or black.
Repetitive pressure from ill-fitting shoes or activities like running can also cause this injury. The pressure from pooled blood can sometimes cause discomfort or pain, which lessens as the injury subsides. Over time, the discolored area will gradually grow out with the nail.
Fungal Infections
Fungal infections (onychomycosis) are a common cause of toenail discoloration. They thrive in warm, moist environments, making toenails susceptible. Fungi can infiltrate the nail, causing changes beyond darkening.
The nail may become thickened, brittle, or crumbly, and its color can shift to yellow, brown, or black. Darkness can result from fungal debris under the nail or separation from its bed. Risk factors include damp conditions, nail damage, and certain health conditions.
Pigmentation Changes and Moles
Dark lines or spots on a toenail can relate to changes in melanin production, the natural pigment for skin and hair color. This phenomenon, melanonychia, can appear as a pigmented band running lengthwise down the nail. In many cases, especially for individuals with darker skin tones, this increased melanin production is harmless and a normal variant.
Benign moles (nevi) can also occur in the nail matrix, leading to a dark streak. However, a rare but serious cause is subungual melanoma, a form of skin cancer. Melanoma characteristics include a rapidly changing dark streak, irregular borders, a width greater than 3 millimeters, or pigmentation spreading from the nail onto surrounding skin.
When to Seek Professional Advice
While many dark toenails are harmless, certain signs indicate that professional medical evaluation is advisable. One sign is if the discoloration does not grow out with the nail over several months. Rapid changes in the appearance of the dark area, such as an increase in size or intensity, also warrant attention.
Pain, swelling, or unusual odor with the dark toenail could suggest an infection or other complication. If a dark streak appears suddenly without any known injury, or if the dark pigment extends from the nail plate onto the adjacent skin, a medical consultation is recommended. Consulting a healthcare provider is also prudent if the cause of the dark toenail is uncertain.