Post inflammatory erythema, whilst common, does sometimes resolve spontaneously over time. I have had patients on Roaccutane (isotretinoin) worried about the erythema as their skin starts to clear and acne heal.
I prefer to get my patients to wait 1 to 3 months for the redness to subside before commencing treatment. There is no evidence to suggest that there is any harm to getting laser treatment done whilst on isotretinoin. My practice is to allow the skin additional time for the redness to subside post medication. It can possibly reduce the number of sessions required since each laser treatment increases blood flow to the area and therefore an increase in the redness immediately post treatment.
That being said, I also treat patient using a non ablative pico-second laser for other skin conditions (tattoo removal) whilst they are on isotretinoin and there have been no ill effects.
Taking a wait and see approach can sometimes reduce the number of treatments required.
