While primary milia is most often seen in infants (pediatric milia) this form may develop on any person of any age and any race. Primary milia develop spontaneously.
It's theorized that primary milia occur in newborns because the sebaceous glands (your oil glands) aren't yet fully developed in infancy, and the skin just isn't able to exfoliate naturally [source: The Permanente Medical Group]. For children and adults, primary milia develops when your dead skin cells and your sweat become trapped in pouches near the surface of your skin, and, without a way of escaping your body, become small cysts of keratin.
Primary and secondary milia may look alike but they aren't caused by the same problem. Let's talk about the reasons we develop secondary milia, next.