Black nails can be a sign of certain conditions on the body. The causes can be due to lack of nutrition, an infection, injury, to some more serious medical conditions such as diabetes, or even melanoma skin cancer. Healthy nail color is generally clear white. Changes in nail color, both finger nails or toes, can be a sign of a problem with your health. In some cases, the color of black nails is not a serious condition and can improve on its own. But in some others, black nails are a sign of a serious medical condition and need immediate doctor treatment. Causes of Black Nails to Watch Out for Below are some conditions that cause the nail to change color to black. Some of them have to watch out for because they have the potential to endanger your health and even your life. Infection One of the most common causes of black nails is a fungal infection. But bacterial infections can also cause nails to turn black. Nail fungus infection occurs when the fungus attacks the fingernai