My DD got a rash with a pacifier (on her chin). So we would dry it and apply aquaphor as a barrier to the moisture. I wouldn't think a barrier applies to a heat rash. I try not to use ointments and such.
TTC#1 2003 BFNs, 2004-2009 5 angels above
2010 IVF-PGS-FET#1, DD b. Aug-2011
TTC#2 2012 BFNs, 2013 FET#2, DS b. Nov-2013
TTC#3 2015 BFNs, FET#3 (my 6th and last angel above)