What might cause my nails to become discolored and black?

Melanonychia is a condition where the nails develop dark streaks or become discolored. This can happen for several reasons:

1. Injury: Sometimes, an injury to the nail can cause bleeding under the nail, leading to a black appearance.

2. Medical Conditions: Some health issues, like fungal infections or certain skin conditions, can also cause nails to change color.

3. Medications: Certain medications might affect nail color as a side effect.

4. Melanonychia: This is a specific condition where there is increased pigment in the nail, often appearing as a dark streak. It can be due to benign causes or more serious concerns like melanoma.

If you notice changes in your nail color, especially if it's a new change, it's a good idea to consult a healthcare professional to determine the cause and get appropriate advice.