A giant screen can magnify even the tiniest facial blemish, so a conspicuous skin condition such as rosacea could become a significant career roadblock for an actress if it goes undiagnosed and untreated. Fortunately for TV, stage and movie actress Cynthia Nixon, co-star of "Sex in the City," a dermatologist was able to put a name to her vexing facial inflammation before her rosacea got out of hand.