Hair follicles don’t grow new hair immediately after hair loss. Based on the law of hair growth cycle, it usually takes about 3 months after hair loss for the hair to start growing out. Hair also has its own growth cycle. The anagen phase lasts for 2~6 years, and this period accounts for about 90% of the total hair volume; the degenerative phase lasts for 2~3 weeks, and this period accounts for about 1% of the total hair volume; the resting phase lasts for about 2~3 months, and this period accounts for about 10% of the total hair volume. When the hair falls out, the hair enters the resting phase and will re-enter the growth phase after 3 months, so it takes about 3 months after hair fall for the hair to start growing out. Although diet and routine can also affect the rate of hair growth, if the hair does not grow back within a year, you need to pay attention to whether permanent hair loss has occurred. In case of abnormal hair loss, it is recommended to go to a regular hospital in time to assess the cause and standardize the treatment under the guidance of a doctor to avoid serious consequences.