What is the term for the darkening of toenails or fingernails?

The term for the darkening of toenails or fingernails is melanonychia. This condition refers specifically to the presence of excess pigmentation in the nail matrix, resulting in a darkened appearance of the nail. Melanonychia can have a variety of causes, including increased melanin production and certain medical conditions or factors such as trauma or systemic disease. Understanding this term is crucial for recognizing potential underlying health issues that may manifest through changes in nail coloration.

Hypopigmentation, while related to pigmentation changes, refers to a reduction of pigment, which is not relevant to darkening. Onychomycosis is a fungal infection that typically causes discoloration but is not synonymous with darkening itself, as it often leads to other changes in the nail's appearance and texture. Paronychia describes inflammation of the skin surrounding the nail, which can sometimes be associated with discoloration but does not inherently refer to the darkening of the nail itself. Therefore, melanonychia is the precise term that encapsulates the idea of darkened nails.