While it is true that the creams, oils and greases used in cosmetics can aggravate acne by irritating or blocking pores, many cosmetics and foundations will not actually cause a flare-up to occur. Many foundations on the market can help to improve the look of acneic skin without clogging pores. If you are concerned and don't want to take a chance, look for products labeled "non-acnegenic" or "non-comedogenic".