Baby sweats easily. He has red patches on his back. Which lotion is best to reduce those heat rash? Or is powder better?

Use moisturiser that can lock in moisture into the skin such as ceradan and apply periodically to prevent dry skin. Wipe away the sweat and keep baby cool. Wear 100% cotton wears. Do not use powder as it will block up the pores making it harder for the skin to breathe or even irritate the skin.