There are many reasons for iron deficiency anemia, which we can categorize into several aspects. The first aspect is a decrease in iron intake, including diet, meaning insufficient dietary intake. The second aspect is decreased absorption, such as the absence of a target organ for absorption or the lack of stomach acid affecting its absorption efficacy. The second aspect refers to excessive loss, most commonly chronic gastrointestinal bleeding, such as in patients with tumors, duodenal ulcers, gastric ulcers, gastritis, ulcerative colitis, a parasitic infection with hookworms, as well as hemorrhoids, and arteriovenous malformations, all of which can cause gastrointestinal bleeding leading to increased iron loss. Excessive menstrual flow in female patients, multiple blood donations, and multiple pregnancies can all lead to iron deficiency. These are the various causes related to iron deficiency.