Anemia can be caused for varies reason know in details:
Anemia due to active & excess Bleeding or Blood loss
Iron-deficiency anemia:
It's most common type of anemia. Happens when do not have enough iron in the body. Iron deficiency is usually due to blood loss or inadequate iron intake or may occasionally be due to poor absorption of iron. It can also occur when there are stomach ulcers or other sources of slow, chronic bleeding (colon cancer, uterine cancer, intestinal polyps, hemorrhoids, etc).
Anemia related to Pregnancy:
Water weight and fluid gain during pregnancy dilute the blood, which may be reflected as anemia since the relative concentration of red blood cells is lower.
Anemia of Chronic disease:
Any long-standing and ongoing medical condition such as a chronic infection or cancer may cause this type of anemia.
Anemia related to Poor nutrition
Sickle cell anemia:
It is typically hereditary and is more common in those of African, Middle Eastern, and Mediterranean ancestry. Abnormal hemoglobin molecules may cause problems in the integrity of the red blood cell structure and they may become crescent-shaped (sickle cells).
Pernicious anemia:
It may be a problem in the stomach or the intestines leading to poor absorption of vitamin B12.
Hemolytic anemia:
It is a type of anemia in which causes for the red blood cells destruction known as hemolysis.