Why is black under my toe nail?

Toenail: If you have recently stubbed the toe or dropped something on it, that could be old blood under the nail. Fungus can grow under a nail and give a black coloration. Sometimes a mole will form at the base of a nail and discolor it as it grows out. See your doctor if you want to get a diagnosis.

Black toenail: A number of things can make a toenail/portion of the toenail look black: fungal infections, blood under nail, certain medications, inflammatory conditions. With meds, most/all nails are involved. Moles/freckles in the nail growth center (matrix) give linear pigmented brown or black streaks, so can melanoma. If the discoloration of the nail is new, please see your dermatologist for proper diagnosis.

Trauma or not?: If it was from trauma i.e. You dropped a brick on it causing a black nail..You will eventually get it back, with a new nail of course. If no trauma at all and just started turning dark underneath slowly and growing, i would have it evaluated for possible melanoma..Subungal melanoma, which is quite rare, but happens..Don't mean to scare you, but that is all i got from your question.. Good luck.

See a podiatrist: If you injured the toenail and it is now black, it is probabley from blood under the toenail. If it is painful, you should have the blood drained. It should be looked at by a podiatrist to determine what to do.