The main cause of a purple tinge in fingernails is low oxygen levels in the blood. This can be caused by poor circulation, as well as habits that inhibit oxygen absorption such as smoking. A single fingernail may also become purple if it has been injured, indicating a bruise underneath the nail.
According to New Health Guide, blood that is rich in oxygen is red. When oxygen levels in blood are reduced, the blood's color darkens. This produces the purple tinge in fingernails if the blood there does not contain enough oxygen. Apart from poor circulation and smoking, lack of oxygen in the blood can also be caused by anemia. Anemia is a lack of iron in the blood and interferes with oxygen absorption.
To treat purple fingernails caused by poor circulation, it is advisable to massage or heat the fingertips. This will help increase circulation. It may also help to carry around a stress ball to squeeze periodically throughout the day. If the purple color is caused by an injury to the fingertip, there is nothing to do but wait for it to heal. If the purple color may be caused by anemia, taking iron supplements and vitamin C may increase oxygen absorption.