Dr. Greene's Answer
If you look at a lot of babies, you will see an amazing variety of hair patterns. Some may be bald as a cue ball while some have thick locks and everything in between. Most babies will have two crops of hair in the first year. In some, that first growth falls out before the second appears and it looks like they are going bald (sometimes this even happens before birth, and the babies are born bald). In others, the second growth comes in while the first is leaving and it is hardly noticed.
There are also other things that can cause hair loss at that age (or accelerate normal hair loss). This includes significant cradle cap. If the scalp or the hairs do not look normal, be sure to point this out to the pediatrician during well-child exams to be sure the hair loss is not being caused by one the many conditions with hair shaft abnormalities, such as monilethrix, pili annulati, trichorrhexis, Menkes disease, etc. Hair loss can be triggered by anything that causes inflammation of the scalp, such as severe cradle cap, skin infections, lupus, etc. Other causes include autoimmune problems (alopecia areata) or as a result of some trauma (including birth trauma) such as telogen effluvium or anagen effluvium.
Hair loss can be the result of a severe nutrition problem as well, such as protein malnutrition, iron deficiency, or zinc deficiency. Also, hormone diseases such as thyroid problems can cause hair loss–and then there is an even longer list of possible hereditary reasons. But as I said, losing a crop of hair is a normal developmental process and is not a cause for concern as long as the scalp and hair shafts look normal.