Polycythemia is a condition characterized by an abnormal increase in red blood cells. It can be primary, caused by bone marrow abnormalities, or secondary, caused by factors like smoking or lung diseases that result in hypoxia. Symptoms include headache, dizziness, and skin redness or itching. Diagnosis involves blood tests showing elevated red blood cell counts. Treatment may include phlebotomy to reduce blood volume, medications to suppress blood cell production, and lifestyle changes like exercise and avoiding tobacco. Nursing care focuses on monitoring for blood clots, managing pain and nutrition, and providing education.