Thinning

During pregnancy, a child has elevated levels of hormones that stimulate the growth of hair. After birth, the baby's hair goes into a resting pattern known as the telogen phase and the hair stops growing and begins to come out.

Normalcy

Hair loss during the first few months is typical, as all babies enter the telogen phase after the pregnancy hormones dissipate from their bodies. If conditions are accompanied by other concerns or happen extremely quickly, a pediatrician should be advised.

Sleep

Babies often lose hair in patches due to their sleep position. Babies put to sleep on their back may rub a bald spot on the back of their heads, and side-sleepers often wear hair off the sides of their heads. Baldness due to sleeping positions is normal and isn't of great concern. It is often called cradle cap.

Treatment

If hair loss is due to sleeping position, alternating sides may help hair grow back without being rubbed off. Hair that grows in its place is usually thicker and may be a different color or texture.

Conditions

Cradle cap, skin infections, high fever or malnutrition may cause erratic or sudden hair loss in babies. These conditions should be evaluated by a pediatrician.

Source:

Hair Today, Gone Tomorrow: The Truth About Infant Hair Loss

Dr. Greene: Infant Hair Loss

BabyCenter: Hair Loss