There are many causes of scalpĀ hair loss, and they do differ in men and women. This website will cover the common ones. Studies show that losing up to 100-150 hairs per day is normal. Human hair naturally grows in three phases: anagen, catagen, and telogen.Anagen is the active or growing phase. Catagen is a fairly short phase of the natural hair cycle during which hairs begin to break down. Telogen is the resting phase. The hairs that are shed daily are often in the resting or late phase in the hair cycle.