Can a postpartum mums use this?

It really depends on which product you are referring to, so it might be hard to give a direct answer without knowing more details. Generally speaking, postpartum bodies are still recovering and some ingredients that are fine normally may not be suitable during that period, especially if you are breastfeeding. I would suggest checking the product label carefully for any warnings related to breastfeeding or postpartum use, and if you are unsure, bringing it up with your doctor or PD at your next visit just to be safe. Better to get a professional opinion since every mum's recovery is different.