Even my babies used to get heat rashes around that age.
Better to take to a doc to make sure its a heat rash and not anything else.Mine didnt give me any medication.
What you can do is...
Dress him in loose cotton clothing.
Dont bathe him in very warm water.This will aggravate the dryness.
Try the Sebamed baby lotion.
Since he is 10 months old,give him water frequently in small amounts.

I applied a cortisone cream on my babies red spots,but you better a check a doctor.