Erythrocytosis, or erythrotosis, is primarily stimulated by increased production of red blood cells in response to low oxygen levels in the blood, a condition known as hypoxia. This can occur due to various factors such as living at high altitudes, chronic lung diseases, or certain heart conditions. Additionally, the hormone erythropoietin (EPO), produced by the kidneys, plays a crucial role in stimulating red blood cell production in the bone marrow. Other factors, such as anabolic steroids or certain tumors, can also lead to increased red blood cell production.