 [ Symptoms ] how long does rash from strep throat last my son is 10 months old diagnosed with thrush was given nystatin rash developed and seems to have worsen with nystatin taken to pediatritian again and son rediagnosed with strep said rash developed from strep concern i have is if rash developed from nystatin or strep if it is from step how long does it usually last [ Disease ] the rash from strep is called scarletina or scarlet fever it would be very uncommon in a ten month old and i would definitely confirm this with a culture this type of rash is bright red covers the entire body and the child is very very ill later this rash will peel like a sunburn and can last a week or more i have no way to examine your child over the internet but i would question the diagnosis thrush is yeast not a bacteria and it does not cause a general skin rash other than a diaper rash the drug nystatin is unlikely to cause a rash