A year or so later, about the age of 15, hair appears in his armpits and some frizzy hair starts tentatively on his upper lip. By now, too, his larynx, or voice-box, has increased in size owing to the circulating testosterone, and his vocal cords have lengthened. These changes deepen the boy’s voice, but for a year or so he may have difficulty in controlling the lower register, so his voice may suddenly jump from deep tones to a high squeak.
Not all the effects of testosterone are so beneficial. The hormone acts on the sebaceous glands in the skin, leading to acne which disfigures the face and neck of many adolescent boys, causing embarrassment and dismay, and making many concerned about their attractiveness to girls.
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