Sometime between 9 and 13, most guys go through puberty, a process that, in essence, changes your body from a child to an adult. Both boys and girls go through puberty.

When a boy starts going through puberty, usually the first thing that happen is hair starts growing under his arms, around his penis area (genitals) and on his face. Hair on other parts of his body will often get thicker and darker, too. Some guys have more hair than others. Genetics play a part in this. That means if your dad, for example, has a lot of body hair, chances are pretty good that you will, too, although that�s not always true.

Also during puberty, a guy�s voice box grows. That�s what causes his voice to crack and squeak. It takes a few months for the cracking to stop, as the voice deepens and settles into its adult tone.

During puberty, it�s also common for boys to have large growth spurts, times when they grow real fast over a short period of time. This rapid growth can cause �growing pains,� when joints and muscles ache and get sore. Also, when a guy grows real fast, he doesn�t have time to get used to his larger limbs. So he sometimes feels awkward and clumsy.

This might seem weird, but, during puberty, some guys develop swollen and tender breasts. If that happens to you, don�t freak. You�re not turning into a girl. Blame the hormones. They�re causing your chest to swell. It�ll go away when the tissue is replaced by muscle. So relax. Because puberty also usually brings guys more muscle and strength.

Another bit of good news. The penis, testicles and scrotum also grow during puberty. The testicles and scrotum start growing and producing sperm. Since your testicles (balls) are growing faster than your penis at first, it might seem like your penis is shrinking. It�s not. In time, it all evens out.