The time for boys to grow armpit hair is usually around the age of 13 to 15 years during puberty, and the exact time varies from person to person. The general order of the development of external genitalia and secondary sexual characteristics in boys is testicular enlargement → scrotal skin changes → penis enlargement → the first appearance of pubic hair → the first appearance of armpit hair → the first appearance of the beard → change of voice → the laryngeal knot. Generally speaking, boys begin to appear pubic hair at the age of 12 to 13 years, while the appearance of armpit hair is 1 to 2 years later than pubic hair. Armpit hair is the hair that grows in the armpits, mainly due to the influence of androgens in the body, which stimulate the hair follicles to start growing and developing, making the armpits grow armpit hair. The growth of armpit hair may also be accompanied by an increase in the amount of sweat in the armpits, an increase in the odor of sweat, and an abnormal taste. Armpit hair is one of the secondary sexual characteristics and appears in most boys at the age of 13 to 15 years. Armpit hair is one of the signs of puberty, and both males and females almost always grow armpit hair. The age of 13 to 15 is only an approximate time. Individuals differ in that some people grow armpit hair early, while others may not grow armpit hair until much later. If you do not have armpit hair, we recommend that you go to the hospital for a checkup to determine the cause.