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

The term for the darkening of the fingernails or toenails is melanonychia. This condition typically occurs when there is an increase in the pigment melanin in the nail matrix, leading to a brown or black discoloration of the nails. It can be a normal variation in some individuals or may indicate a medical condition that should be evaluated, such as a benign lesion or in rare cases, melanoma. Understanding this term is important for cosmetology professionals as it helps in identifying potential concerns during nail examinations.

The other terms listed do not accurately describe the darkening of the nails: onychomycosis refers to a fungal infection of the nails, chromonychia is somewhat of a less commonly used term that can refer to color changes in the nails but is not specific to darkening, and achromia describes a lack of color, which is the opposite of darkening.