Many of the changes take place on the outside. But, there are inside changes too! The pituitary gland (pi-TYOU-uh-terr-ee) at the base of your brain announces puberty to your body. Hormones are the chemicals inside your body that carry the message. One important hormone called testosterone (tes-TOS-tur-own) steps up and takes charge of growth. Testosterone makes the penis and testicles (external genitalia) grow and it helps the testicles produce sperm. It's also responsible for hair growth on a boy's chest, legs, face, and under the arms. Hair also starts growing around the penis and scrotum. These short, curly hairs are pubic hairs, and they get thicker during puberty.

Hormones do another important job! They are responsible for making oil and sweat glands work. And they can change boy's feelings about friends AND girls.

Puberty is easy to spot. A guy's larynx (voice box; when it grows and shows as a bump on your neck, it's called an "Adam's Apple") is growing and makes his voice start to crack and squeak before it deepens. Muscles develop and growth spurts happen. The chest area swells slightly, and nipples feel more sensitive. Hardening in the nickel-sized area around the nipple is a totally normal sensation Testicles grow larger and hang lower. The penis also grows longer and the skin darkens in color. Whew! Let's take a breath here because that's a whole lot of changes to absorb. Now, moving on…umm, maybe moving down is a better way to describe this next section.