Thank you for your query.
You have not mentioned the duration of the problem or any other associated symptom like fever
, etc. If there is no improvement after giving Piriton
then your daughter would need to be investigated furhter for the cause. I suggest you follow up with the treating doctor.
If it is heat rash
then there should be itching and the child will be comfortable in a cooler environment. If it a reaction to something then the offending item needs to be identified by exclusion.
I hope I have answered your query to your satisfaction.
Wishing your daughter an early recovery.