I have read that Ichthyosis Vulgaris (IV) symptoms first appear between ages 2 and 5. My own mother told me that I was not born with scaly skin and that it appeared later.

My question is: what prevents the symptoms of IV from appearing in the first few years of life? After all, the defective FLG genes are there from birth itself. So is it something in breast milk which prevents the baby's skin from getting scaly?