A toenail turning black can be a concerning change. This alteration in nail color can stem from various sources, ranging from minor and temporary issues to more serious underlying health conditions. Understanding the potential reasons behind this discoloration can help in determining the appropriate course of action.
Trauma and Bruising
The most common cause of a black toenail is a subungual hematoma, which is essentially a bruise under the nail. This occurs when small blood vessels beneath the nail plate rupture, leading to blood pooling in the confined space. Acute injuries, such as stubbing a toe forcefully or dropping a heavy object directly onto the foot, can cause this sudden bleeding.
Repetitive micro-trauma can also lead to subungual hematomas, often seen in athletes, particularly long-distance runners. Ill-fitting footwear can cause consistent pressure and friction on the toes. As blood collects under the nail, the color progresses from dark red or purple to dark brown or black as it coagulates. This discoloration will grow out with the nail over several months, taking 6 to 9 months for a new nail to replace the affected one.
Fungal Infections
While often associated with yellow, white, or brown discoloration, fungal infections of the toenail, known as onychomycosis, can also sometimes present with a black appearance. This darkening can occur as the infection progresses, or due to debris accumulating under the nail. These fungi, such as dermatophytes, thrive in warm, moist environments, making toenails particularly susceptible.
An infected nail may become thickened, brittle, or crumbly, and its shape might change. A foul odor can also be present. Individuals with certain conditions like diabetes or compromised immune systems may have an increased susceptibility to these infections.
Underlying Medical Conditions
A dark discoloration of the toenail can sometimes indicate more serious underlying medical conditions. Subungual melanoma, a rare form of skin cancer, develops under the nail and can appear as a dark, spreading streak or patch. This discoloration often runs vertically, from the cuticle to the tip of the nail, and may widen or become irregular over time. Unlike a bruise from trauma, melanoma typically does not resolve or grow out with the nail.
Less common systemic conditions or medication side effects can cause nail discoloration. Certain drug reactions, autoimmune diseases like psoriasis or lupus, or circulatory problems such as peripheral arterial disease, may cause changes in nail color or texture. While these conditions might cause general nail changes, a black appearance is less typical compared to trauma or melanoma.
When to Seek Medical Attention
Consult a healthcare provider for a black toenail in several situations:
- If the black area appeared without known injury or trauma.
- If it is spreading or changing in size or shape.
- If the blackness is accompanied by increasing pain, swelling, pus, or a foul odor, which could indicate an infection.
- If the nail appears to be lifting from the nail bed.
- If the discoloration does not improve or grow out with the nail over several months.
- If a dark streak extends from the nail into the cuticle or the surrounding skin, known as Hutchinson’s sign, as this requires immediate attention.