Brief Answer:
Can be infective, please provide pictures

Detailed Answer:
Hi

Pigmentation or black discoloration of toe nail can point towards various possible causes.
It can occur due to any trauma to nail leading to a small hemorrhage underneath the nail. It can be due to a toe nail infection like fungal or it can be due to other local and systemic causes.
I would like to have a look at the exact nail conditio n . Please click some close up pictures of the nail and upload them here on this page.
Also tell since when do you have this discoloration?
Is it only on a single nail?
Developed suddenly or slowly increasing?
Any pain or discomfort?
Is the surrounding skin normal? Any swelling of nail folds?

I am sure I will be able to help you more once you provide me the above details and the pictures .

Dr Geetika Paul

---