If I have rosacea or perioral dermatitis, haven't been diagnosed, my doctor has given me fucibet cream to use for 7-10 days, but then it comes back...

Rosacea and steroids. Steroids like those in fucibet can make rosacea significantly worse. When you apply a steroid cream to the skin, it constricts blood vessels for several hours making rosacea appear better temporarily. Over time these blood vessels dilate even more with topical steroids. Also steroids increase numbers of demodex mites in hair follicles also worsening rosacea.