The sudden yellowing of the hair may be due to pathological factors and lifestyle habits. 1. Pathological factors: mostly caused by malnutrition, which can lead to hair brittle, yellow, and may be due to nutritional disorders caused by hypothyroidism, the recent hemorrhage can also lead to anemia and then manifested as yellow hair, mostly seen after childbirth or major surgery. 2. Lifestyle habits: if long-term perm, hair coloring habits, will lead to dry, yellow hair, or hair long-term exposure to the sun, swimming, etc. will also lead to yellow hair phenomenon. Sudden yellowing of hair may also have other reasons, it is recommended to consult a professional doctor in a timely manner in a regular hospital for relevant examinations and targeted treatment.