Health Conditions Black Line on the Nail: Should You Worry? by Miral khattak May 24, 2024 by Miral khattak May 24, 2024 A small black line that runs vertically under your nail could be a splinter haemorrhage. Lines that run horizontally could be melanonychia. These could be no big deal or a … 0 FacebookTwitterPinterestLinkedinWhatsappEmail