How long does it take for a scabies rash to go away after treatment?

Scabies. Although sometimes referred to as the "seven-year itch, " scabies can be effectively treated with killing of the mite sarcoptes scabiei, preventing cross-contamination from a close contact and/or clothes/bedding sheets. Sometimes pruritus may be secondary to postscabetic dermatitis which in turn is secondary to the skin reaction to the scabies infestation that persists after effective eradication.
Usually 2-4 wks. Depending on the severity of the lesions, average out i would say 2-4 wks after successful treatment/erradication of the scaby mite--sarcoptes. The more severe/large/deep the lesion, the longer it will take to heal. At times treatment may need to be repeated or even oral medication may be needed. Make sure other family members r treated at same time and do pest-control measure. Good luck.