Newborn baby hair loss is perfectly normal and nothing to worry about. Babies often lose their hair during the first six months. This kind of hair loss is called telogen effluvium.

Here's why it happens: Hair has a growth stage and a resting stage. The growth stage lasts about three years, and the resting stage lasts about three months (although anywhere from one to six months is normal). During the resting stage, the hair remains in the follicle until the new hair starts coming in.

About 5 to 15 percent of hair on the scalp is usually in the resting phase at any one time, but stress, fever, or a hormonal change can cause a large number of hairs to stop growing all at once. The shedding begins when the next growth stage starts up about three months later.

A newborn's hormone levels drop right after birth, which can cause him to lose the hair he was born with. (New moms often lose large amounts of hair for the same reason.)

Parents are sometimes surprised to discover that when a baby grows a new head of hair it's a completely different color and texture than what he was born with. BabyCenter reader Julie's son Will was born with a full head of thick black hair. "He looked just like Elvis — he even had sideburns," she says. "Both my husband and I are blond, and we wondered where the dark hair came from. Almost immediately after birth, though, it started falling out. The hair that replaced it is a beautiful wheat color."

If you notice that your baby has bald patches, observe the way he sits and sleeps. If he always sleeps in the same position or tends to sit with the back of his head against a baby seat, he may lose hair in that area. He may also develop a bald spot if he rubs his head against his mattress.