Do NOT use creams to prevent heat rash. They block the pores and keep moisture in. They are great for diaper rash or eczema, not heat rash. Certain ointments can help with itching after it occurs. Look it up (Google "prickly heat or heat rash in babies") or ask your pediatrician.
Heat rash(prickly heat) is caused by the infants inability to sweat. When you use creams, you will add to the problem.
I agree with the previous post....only cotton! I always check the material on clothes before putting them on my kids in the hot houston weather.....many clothes are half polyester, big no-no as well as any synthetic materials.
Also, I took my newborn for morning walks after I had her. It was April, not too hot but she got prickly heat rash. I felt bad b/c I thought it was my fault for letting her get overheated.
Reminder to Mom's----those deep strollers we put the babies in do NOT get the air flow, breezes, etc. that we experience when walking. To me, the stroller can be a little "oven" and that's when my baby got her heat rash.
Then on top of it, some Mom's put blankets over the stroller ---hot, hot, hot!!
Those little babies can't sweat like we do and their body can't cool itself down as we can.