Onychomycosis is a common fungal infection that affects the nail unit. While it is more frequently observed in toenails, it can also affect the fingernails. This condition is caused by various fungal organisms, most commonly dermatophytes, though yeasts and non-dermatophyte molds can also be responsible. The appearance of an infected fingernail changes significantly as the fungus invades the nail plate and the underlying nail bed. Recognizing these visual changes is the first step in identifying the infection. Early detection is helpful because the fungus degrades the nail’s keratin, making the infection progressive and increasingly difficult to treat as it advances.
Early Signs of Fingernail Infection
The initial stages of a fungal infection in a fingernail can be subtle, often beginning with a minor visual change. One of the first indicators is a loss of the nail’s natural luster, giving the surface a dull or opaque appearance. This early phase may also present as a slight, fine powdery texture on the nail plate’s surface.
The infection often starts in a localized area, appearing as a small, white or yellow-brown spot. This discoloration typically begins near the edge of the nail, either at the tip or along the side, where the fungus first gains access to the nail unit. These small spots indicate the fungus is establishing itself in the superficial layers.
The infection may also cause minor irregularities in the nail’s texture. Slight striations or pitting can appear on the nail surface. These physical changes reflect the fungal organism beginning to break down the protective keratin structure.
Physical Changes in Nail Structure
Hyperkeratosis
One of the most noticeable advanced symptoms is hyperkeratosis, the severe thickening of the nail. This thickening occurs as the nail bed reacts to the infection by producing an excessive amount of keratinous debris underneath the nail plate. The accumulation of this chalky, dense material elevates the nail plate, causing it to become misshapen and difficult to trim. In severe cases, this buildup can be so substantial that it causes discomfort or pressure. The fungus degrades the nail’s protein, leading to a brittle and crumbly texture, especially at the edges.
Onycholysis
The physical damage also frequently leads to onycholysis, which is the separation of the nail plate from the nail bed. This separation typically starts at the free edge of the nail and progresses backward toward the cuticle. The newly created space under the nail appears white or opaque because of trapped air and debris, and it can serve as a reservoir for further fungal and bacterial growth. This structural breakdown is a hallmark of an established fungal infection. In the most advanced stage, known as total dystrophic onychomycosis, the entire nail plate is destroyed, becoming thick, brittle, and severely deformed.
Types of Discoloration
While structural changes are pronounced, the visual appearance of nail fungus is often defined by distinct patterns of discoloration. The most common color change is a yellow or yellow-brown hue, which often starts under the tip of the nail. This discoloration is the result of fungal debris and the byproducts of the keratin degradation process within the nail bed.
White spots or streaks are also a frequent visual sign, particularly in a form known as superficial onychomycosis. In this type, the fungus invades the top layer of the nail plate, creating islands of white, chalky material on the surface. These white patches can sometimes be scraped away, distinguishing them from deeper infections.
Less common are green or black discolorations that indicate the presence of other organisms. A green color is often caused by a secondary bacterial infection, most commonly Pseudomonas aeruginosa, which thrives in the moist space created by nail separation (onycholysis). Black discoloration may be due to specific types of molds or the accumulation of dark debris and blood under the nail plate.