Reaction to a medicine and lack of adequate oxygen in the blood may cause blue fingernails, explains WebMD. Medical conditions such as Wilson's disease, subungual hematoma, methemoglobinemia and fracture could cause blue fingernails, according to Right Diagnosis.
Asthma, peripheral arterial disease and severe anemia are among the common diseases that reduce oxygen in the blood leading to blue fingernails, notes WebMD. In this case, it's a form of cyanosis. Lung disease, emphysema and failure of the heart to pump blood to all body parts can also cause blue fingernails, explains eVitamins. Other diseases or conditions that can cause blue fingernails include agyria and silver poisoning, states Right Diagnosis.