There are two main types of polycythemia. Absolute polycythemia can happen when the body makes more red blood cells than usual. This can be due to gene changes or various health problems, including blood cancer. Relative polycythemia can happen when the volume of plasma, which is the liquid part of blood, falls. Causes can include certain medicines, vomiting and smoking.

Polycythemia doesn't always lead to symptoms. When it does, the symptoms depend on the underlying cause. Some of the many possible symptoms include stomach or muscle pain, tiredness, slowed thinking, headaches, weight loss, or bruised or itchy skin. Sometimes, polycythemia leads to emergencies such as chest pain or loss of blood flow to the brain.

It's important to find and treat the underlying cause of polycythemia. Depending on the cause, treatment may ease or get rid of the symptoms of polycythemia. Treatments may include various medicines, procedures or lifestyle changes.