babies and no hair

I'm sure someone can easily answer this, but it has been on my mind the past few days. When a baby is born a lot of them have very fine thin hair, then as they get older they start to grow hair and it becomes thicker. Well what is the baby missing when it is first born that causes the hair to be so thin? Whatever the baby is lacking could be the same that is causing mpb. I know its a pretty silly question but I was curious to see if there was any connection.

i think babies have villus hairs because the hair follicles have not been fully developed. i dont think you can tie an under developled hair follicle to mpb. just my opinion.

Often the very fine vellous hairs that infants have at birth shed and are eventually replaced with terminal hairs. I do not think that the thin hairs get thicker.