1, infants and children are commonly improperly fed, not adding complementary foods in a timely manner, or improperly added complementary foods. 2, adolescents are common picky eaters 3, women of childbearing age, common excessive menstruation, and iron-containing foods eaten less. 4, adult men, postmenopausal elderly women, pay attention to the chronic blood loss in the digestive tract, commonly tumors, hemorrhoids . 5, rare causes, post-operative gastrointestinal tract, iron absorption disorders. 6, the author has seen a case of severe psoriasis, a large number of dandruff caused by the loss of iron.