Federal health officials are warning consumers who use popular anti-acne treatments about rare but potentially deadly allergic reactions that can cause swelling of the face and difficulty breathing. The Food and Drug Administration said on Wednesday that the problems had been reported with gels, face washes, pads and other products that contained two ingredients: benzoyl peroxide or salicylic acid. But the agency says it was unclear whether those ingredients set off the reactions or whether some other combination of ingredients was to blame. The over-the-counter treatments are sold as Proactiv, Neutrogena, MaxClarity, Oxy, Aveeno and other brands. For now, the agency wants consumers to stop using the products if they experience tightness of the throat, breathing problems, lightheadedness or swelling of the eyes, face or lips.