Hair loss is considered to be related to factors such as baldness, androgenetic alopecia, and acute resting hair loss. Through hair follicle testing, the cause of hair loss may be found out. 1. Patchy baldness: Patchy baldness, also commonly known as ghost shaving, is a sudden onset of limited, patchy hair loss, and patients usually have no other uncomfortable symptoms. It can be examined by trichoscopy, and the performance of trichoscopy may show certain yellow dot sign, black dot sign or produce broken phenomenon. 2. Androgenetic alopecia: Androgenetic alopecia is hair loss caused by excessive secretion of androgens in the body, usually refers to hereditary hair loss in men. Through hair follicle testing, an increase in the number of hair shafts with different thicknesses and thinner diameters may be found. If there is plucking ringworm, dermoscopy will show a clear black spot sign and more broken hairs. 3. Acute resting alopecia: In acute resting alopecia, when detected by trichoscopy, a large number of short, neoplastic hairs may be found, and the hairs are in the form of thinning at the top and coarsening at the bottom. Hair loss is relatively common in clinical practice. Physiologic alopecia is a normal manifestation and generally does not require special treatment. If the number of hair loss is large, it is necessary to go to the dermatology department of the hospital for examination and standardized treatment under the guidance of the doctor after a clear diagnosis.