Hair falling out excessively can be caused by a variety of factors, including genetics, hormonal changes, medical conditions, stress, poor nutrition, and certain hairstyles or chemical treatments. Common causes include hereditary hair loss (androgenetic alopecia), hormonal imbalances such as those related to pregnancy or thyroid issues, autoimmune conditions like alopecia areata, and physical or emotional stress which can trigger telogen effluvium, a temporary shedding condition. Additionally, medication side effects, nutritional deficiencies, and hairstyles that pull hair tightly (traction alopecia) can contribute to increased hair loss.