Healthy nails can reflect overall skin and systemic health. Nail disorders may develop from infection, inflammation, trauma, aging, or systemic disease and commonly cause discoloration, thickening, brittleness, lifting of the nail plate, deformity, or discomfort. One of the most common nail diseases is onychomycosis, a fungal infection that most often affects the toenails but can also involve fingernails.

Onychomycosis (Fungal Nail Infection)

Onychomycosis is caused by three main groups of fungi: dermatophytes, non-dermatophyte molds, and yeasts. Dermatophytes are the most common cause worldwide, particularly Trichophyton rubrum, which digests keratin and gradually destroys the nail. Other dermatophytes include T. mentagrophytes (interdigitale), Epidermophyton floccosum, and occasionally Microsporum species. Non-dermatophyte molds such as Scopulariopsis, Aspergillus, Fusarium, Acremonium, Onychocola, and Alternaria usually infect nails already damaged by trauma or disease and are more often seen in toenails. Because molds can sometimes contaminate nail samples, diagnosis often requires repeat cultures and clinical correlation. Yeasts, especially Candida albicans, more commonly affect fingernails and are associated with chronic paronychia, frequent water exposure, diabetes, or immunosuppression.