This New York Times article provides a great discussion of the treatment of nasal pores:

http://www.nytimes.com/2011/06/02/fashion/many-seek-to-minimize-enlarged-pores-for-a-flawless-look.html?hpw

The long and short of the answer is that with time all of our pores begin to enlarge. Maintenance treatments to cleanse and exfoliate the pores makes them look smaller. In my practice I have I have found that superficial chemical peels or prescription trenitoin (retin-A) can help with this process. Such superficial peels take just a few minutes in the office and require no anesthesia. Trenitoin, a vitamin A derivative, has many skin benefits including the ability to even out the skin tone, improve fine lines, and help with collagen production. It can take a while for your skin to grow acustomed to the medicine, but with time can give very impressive improvements to your skin.