Which of the following is a common nail disorder?

Onychomycosis is a prevalent nail disorder characterized by a fungal infection that affects the nails. It is commonly seen in both toenails and fingernails and can lead to symptoms such as discoloration, thickening, and potential separation of the nail from the nail bed. This condition is particularly important to recognize in a manicure and pedicure context because it can affect the health and appearance of the nails, requiring specific treatment and care.

Psoriasis, while it can affect the nails, primarily manifests as a skin condition and may not be classified specifically as a nail disorder in the direct sense. Athlete's foot is a fungal infection affecting the skin of the feet, and while it can lead to complications with nail conditions, it is not categorized as a nail disorder itself. Contact dermatitis refers to skin inflammation caused by contact with allergens or irritants and does not directly pertain to the nails as a nail disorder. Understanding onychomycosis is crucial for effective nail care practice, as it influences both health and aesthetics in manicures and pedicures.