 [ 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 ] maybe but you will need to be carefully examined some cysts will spontaneous drain or rupture some may become secondarily infected and some may require surgical intervention