The idea that pores open and close has never seemed possible to me because it would require some type of muscle action. A quick google search turns up several discussions that say it is a myth or old wives tale.
Pores can be blocked by dirt, dead skin cells etc that can be removed by cleaning, but I think this might be a good place to stop perpetuating the myth that pores can snap shut or open.
Tom--- Founding member of The ALPHA Team!
If laughter is the best medicine then why do sick people go to doctors instead of comedians?