- Onychomycosis is a common nail disease responsible for approximately 50% of diseases of the nail. It occurs more in the elderly, though several cases have been reported among children. Several factors influence, such as climate, geography, and migration. The two dermatophytes most commonly implicated in onychomycosis are Trichophyton rubrum and T. mentagrophytes, accounting for more than 90% of onychomycoses. Nonetheless, several other toxigenic molds have been implicated. For convenience, onychomycosis is divided into four major clinical presentations: distal subungal, which is the most common form of the disease; proximal subungal, which is the most common form found in patients with human immunodeficiency virus infection; superficial; and total dystrophic onychomycosis. Epidemiology of onychomycosis in adults and children is evaluated and the most common clinical symptoms addressed. Although the risk factors are discussed, the multifactorial nature of onychomycosis makes this inexhaustible. The diagnosis and treatments are difficult and the choice of appropriate antifungal drugs complex and require the knowledge of the chemical structures of the metabolites of the molds that cause onychomycosis and their interaction with the antifungal drugs. This is true because most of the antifungal drugs are derived from mold/fungal metabolism. Treatment with griseofulvin and amphotericin is displaced by the use of newer drugs from azole compounds, pyrimidines, and allylamines derivatives. Amorolfine, itraconazole, and ciclopirox nail lacquer solution 8 have gained support globally, but the side effects, drug resistance, and persistence of the disease are still a serious concern to the patients, just as economics and quality of life. Hence, the search for safer and more efficacious drug treatments are continuing.