When my younger daughter is teething, she drools a lot and sometimes gets a slight rash on her bum which also seems to spread to her body (it is not very noticeable, just some light reddish bumps but it is not itchy).  It doesn't bother her and she is never scratching herself but I did some research online and found an Indian remedy.  All you do is cook some plain white rice and feed it to your child.   I don't really measure it out but my guess is about 2 tablespoons of rice works for my 21 month old.  To make it appealing for her to gobble up,  I put some butter on it so she'll eat more and a few hours later her rash is gone.  The reason is b/c when they drool more, it creates more acidity that enters the tummy when swallowed and it comes out in the urine and that imbalance creates a rash.  The rice soaks up the acid in the tummy and sort of balances everything out so the rash disappears.  I am not a doctor, just simply a mom who found this remedy online and tried it but I would still call a doctor if you felt your child's rash was serious.  If you try this, amounts of rice may vary per kid but believe me, I was surprised when I tried it and what an easy way to get rid of a simple diaper rash.