Contrary to popular belief, pores do not open or close! The size of your pores are genetically programmed and/or stretched by an accumulation of oil and dead skin cells. Once they are strectched they will not close aka get smaller. As you age, pores also get larger because the openings loosen up.
The best way to prevent large pores is to wash with a product that prevents oil build-up as well as promotes cell turnover -one with salicylic acid for oil control and glycolic acid to accelerate dead skin cell turnover. Using of a mild Buf Puff will also work to remove oil and dead skin cell build-up in the pores that causes the pores to be strectched. The old cold water trick helps the appearance by contracting the blood vessels making the skin appear tighter while a moisturizer plumps the skin surrounding the pores also making it appear smaller. Home microdermabrasion kits can also help keep pores clean and taut.
For those with oily skin, and prone to larger pores especially around the nose, cheeks and chin, monthly facials with extractions can be a real benefit