 [ Symptoms ] can powder with cornstarch like gold bond baby powder help with a 3 year olds heat rash under her arms  my granddaughter has a rash under the arms that looks like a heat rash can powder like gold bond baby powder with cornstarch help she is 3 years old thankyou [ Disease ] aw poor baby you should be pretty safe using a product like baby powder or even plain cornstarch out of the box to treat this possible heat rash if the rash does not clear up within the day you might keep an eye on it it is likely nothing serious but it could be something along the lines of a fungal infection similar to athlete is foot be sure to gently cleanse the area with cool water and a mild soap most important pat it dry thoroughly do not rub because it will hurt  as i am sure you know it is not at all unusual for toddlers to develop weird skin rashes that sort of come and go they are usually only problematic when they refuse to go  or if the rash is accompanied by fever in that case it is time to visit the doctor wishing you and your granddaughter well