Larynx changes during puberty cause boy's voice to crack
Q: My son is 14, and his voice has started to change. Why does this happen?
A: Your son is going through puberty. A change in his voice is just one of several changes in this phase of life.
The first thing that generally happens to a boy during puberty is that his testicles begin to get larger and to make testosterone. Then, the penis begins to grow and sexual hair begins to appear. He will become more muscular. He will have more frequent erections, become capable of making sperm and thus become fertile.
Boys undergo a growth spurt during puberty. The bones get longer and then wider. Along with the growth of muscles and bones, there is an even greater growth in the amount of body fat. As a result, body fat becomes a greater fraction of total body weight during puberty.
There also are changes in the heart and blood vessels. Boys develop a greater aerobic capacity, and blood pressure rises slightly.
The reason much of this happens is, in part, rising levels of testosterone. In particular, the increase in this hormone causes changes in the larynx, or voice box. That's what is causing the change in his voice.
The larynx is located in the throat at the top of the trachea, or windpipe. The larynx contains the vocal cords, two tiny muscles. These two muscles tighten and relax to change how air passes through the larynx.
When you raise or lower the pitch of your voice, it is the tightness of the vocal cords that causes the pitch to change. So, changes in the larynx or vocal cords affect your voice.
During puberty, testosterone causes a boy's larynx to get bigger. The vocal cords also lengthen and thicken in response to testosterone.
Just as the shortest strings on a harp or piano make the highest sounds, the short vocal cords of children produce voices that are high in pitch. The longer cords of adult males produce lower-pitched voices.
As the larynx and vocal cords are going through this growth phase, the changes can cause the voice to "crack." The change of voice can happen quickly; over only a few weeks or months, the voice begins to crack and then becomes deeper and more resonant.
As girls go through puberty, their vocal cords also lengthen. But the growth is more modest, so their voice changes are not as noticeable.
If a boy does not go through puberty because of a deficiency of testosterone, his voice will remain high. In fact, in 16th-, 17th- and 18th-century Italy, young boys with a talent for singing operatic or religious music were sometimes castrated. The resulting failure of testosterone levels to rise preserved the high pitch of the boys' voices into adulthood.
There's nothing a boy can do to prevent his voice from cracking as he goes through puberty. If it is making your son uncomfortable, remind him that this happens to all teenage boys and will pass soon enough.
• Dr. Anthony Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.