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Onychomycosis

Onychomycosis signs & symptoms

What are the early symptoms of onychomycosis?

In its initial stages, onychomycosis is usually subtle and may go unnoticed, as it rarely causes discomfort early on. Many people first observe a mild cosmetic change in a single nail, most often a toenail such as the big toe. Early indicators can include: 

Slight discolouration

A small patch may turn off-white, yellowish, or lightly brown, usually at the tip or along one side.

Loss of natural shine

The surface can appear dull, chalky, or cloudy rather than smooth and glossy.

Mild thickening

 The affected nail may feel a little firmer or thicker than others.

Fragile or rough edges

The free edges may chip, split, or crumble more easily than usual.

Fine debris beneath the nail

Soft, powdery material may begin to collect under the tip of the nail.

 

At this stage, the infection is generally painless and may involve only part of one nail. Some individuals also experience athlete’s foot at the same time, with dry or itchy skin between the toes, and this infection can then spread to the nails.

Despite the mild appearance, guidelines advise confirming the diagnosis of onychomycosis before beginning treatment, particularly when considering long courses of oral antifungal medicines. Confirmation typically involves examining a nail clipping or a sample of subungual debris under a microscope or sending it for culture, histology, or molecular testing. 

What are the signs of advanced onychomycosis?

Without treatment—or if treatment is ineffective—the infection can gradually extend deeper and wider, affecting more of the nail plate, multiple nails or even the nail matrix. Advanced disease may present as follows: 

More obvious discolouration

Nails can turn yellow, brown or grey, sometimes with streaks or mixed shades. In severe cases, the nail may become almost opaque

Significant thickening and distortion

The nail may become markedly thick, uneven or curved, making trimming difficult.

Onycholysis

The nail may lift away from the nail bed, creating a space where further debris can accumulate.

Crumbling or breaking

Parts of the nail may fragment or break off, leaving a jagged outline.

Subungual build-up

Keratin and fungal material may collect underneath the nail, often appearing yellow-white and compacted.

Pain or pressure

Thick, misshapen nails may press against footwear, causing discomfort, difficulty walking or problems wearing certain shoes.

Because these conditions overlap in their appearance, current clinical guidance stresses the importance of mycological testing using microscopy, cultures, histology, or molecular methods, before starting systemic antifungal treatment, especially in atypical or stubborn cases.

What can be mistaken for onychomycosis?

A wide range of nail disorders can closely resemble fungal nail infections, and studies show that many nail issues are not due to fungi at all. Because treatment for onychomycosis often requires prolonged therapy,  it is crucial to explore alternative explanations and confirm the diagnosis when necessary.

Some conditions that can be confused with onychomycosis are: 

 

 

Nail psoriasis

Can cause pitting, discolouration, subungual hyperkeratosis and onycholysis. Thickened, discoloured toenails can appear very similar to fungal infection.

Lichen planus and eczema of the nail unit

These may produce ridging, splitting, roughness and thickening, often with chronic inflammation around the nail folds.

Chronic trauma and mechanical changes

Pressure from shoes, sporting activities, toe deformities or gait abnormalities can cause nail distortion and colour changes that mimic fungal disease.

Chronic paronychia and bacterial colonization

Recurrent inflammation around the nail—especially in people with prolonged exposure to moisture—can change nail appearance. Infection with Pseudomonas can produce a characteristic green tint.

Age-related changes and onychogryphosis

Older adults often develop thick, curved or discoloured nails without an underlying fungal cause, although fungi may colonize already abnormal nails.

Subungual haematoma and pigmentary lesions

Dried blood beneath the nail after an injury may look dark brown or black. Any persistent or irregular pigmentation, particularly widening bands, warrants urgent assessment to rule out subungual melanoma.

 

Because these conditions overlap in their appearance, current clinical guidance stresses the importance of mycological testing such as microscopy, culture, histology or molecular methods, before starting systemic antifungal treatment, especially in atypical or stubborn cases. 

If you notice ongoing nail changes, involvement of multiple nails, pain, or any dark or rapidly evolving pigmentation under a nail, you should seek medical advice for proper evaluation. 

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