41year old caucasian in good health, i have a dark line running from cuticle to fingertip on my thumb and index finger..should i be concerned?

Melanonychia: Melanonychia is brown or black pigmentation of the nail unit. Melanonychia commonly presents as pigmented band arranged lengthwise along the nail unit, and this presentation is known as longitudinal (lm) melanonychia or melanonychia striata. The most important cause of melanonychia is subungual melanoma, although there are a variety of other causes.