Onychomycosis, commonly known as nail fungus, is a frequent infection that causes distinct visual changes to the nail unit. These noticeable alterations are often the first indication that something is wrong. The appearance of the fungus is not uniform and changes depending on the specific type of infection and how long it has been present.
The Most Common Visual Signs
The most prevalent form, distal subungual onychomycosis (DSO), typically begins with a change in color and texture at the nail’s farthest edge. This often appears as a white, yellow, or brown patch starting near the tip and along the sides. This discoloration results from fungal organisms invading the nail bed beneath the plate.
As the infection progresses, a chalky buildup called subungual hyperkeratosis develops underneath the free edge. This material, composed of keratin debris and fungal elements, causes the nail plate to lift and become thickened. This thickening can make the nail difficult to trim and may cause discomfort when wearing shoes.
The infected nail often loses its natural translucence, becoming opaque or dull in appearance. This shift results in a discolored, raised, and dense nail, contrasting sharply with a clear, healthy one.
Patterns of Fungal Growth
Fungal infections present in different patterns based on where the organism initially enters the nail unit. White Superficial Onychomycosis (WSO) affects only the outermost surface of the nail plate, appearing as small, opaque white spots or patches. These spots are often powdery or chalky to the touch.
The infected material can often be easily scraped away from the surface, indicating the infection is superficial. While the nail plate may become rough or crumbly, it usually avoids the extreme thickening or lifting seen in DSO.
Proximal Subungual Onychomycosis (PSO) is a less common pattern where the fungus enters the nail from the cuticle area at the base. This appears as a white or yellowish spot that begins near the nail fold and grows outward. Since the infection begins at the nail matrix, PSO may indicate a compromised immune system.
Changes to the Nail Structure
As the fungal infection advances, it compromises the structural integrity of the nail. The nail plate often becomes brittle, with ragged edges prone to crumbling due to the weakening of the keratin structure.
Onycholysis is a significant structural change involving the separation or lifting of the nail plate from the nail bed. Visually, this detachment appears as an opaque white or yellow area, often starting at the tip and moving toward the cuticle. This lifting creates a space beneath the nail where debris and fungi accumulate.
In advanced cases, the entire nail plate may be destroyed, resulting in a thickened, misshapen stump known as total dystrophic onychomycosis. Infections caused by molds or yeast can also produce a foul odor due to the accumulation of infected debris.
How Fungal Appearance Differs From Other Conditions
Many non-fungal conditions can mimic the appearance of onychomycosis, making visual distinction necessary. Trauma or injury typically results in a localized discoloration, often a red or black bruise (subungual hematoma) that grows out with the nail. Unlike the spreading, irregular nature of fungus, trauma presents as a clear, defined line of damage.
Nail psoriasis, an autoimmune condition, can also cause thickening and separation, but it includes unique visual markers. Psoriasis causes nail pitting (small, pinprick-like dents) and “oil drop” spots (translucent yellowish-pink patches in the nail bed). These features are absent in a primary fungal infection.
Age-related changes can cause the nail to thicken and develop vertical ridges, but this process lacks the distinct yellow-brown discoloration or crumbly texture of an active infection. Unlike fungal invasion, age-related thickening does not involve the accumulation of subungual debris.