A number of things can cause dilated pores. A build-up of oil and dirt in the skin can contribute to making pores appear enlarged as they become blocked and the skin around the pores dilates.
People with naturally oilier skin may be more likely to have larger pores because their oil glands are more active, meaning they need a bigger pore to release oil from within the skin.
Aging can also have an impact on pore size. As collagen begins to break down, a lack of elasticity and tautness is created causing the pores to dilate.
Unfortunately, because enlarged pores are largely determined by genetics, we can never physically shrink them, but we can effectively minimize their appearance by keeping them clean and free from build-up of dirt and dead skin cells. Acids like glycolic acid, salicylic acid, lactic acid, and vitamin A have a resurfacing effect on the skin, sweeping away dead skin cells and stimulating cell renewal for a smoother skin appearance.
Salicylic acid is truly a miracle-working ingredient for blackheads and can be an effective tool for minimizing the appearance of pores, blackheads, breakouts, oil, and cleansing the skin. It is an oil-soluble acid, meaning it can penetrate deeper into the skin to exfoliate, unclog, control oil, prevent future breakouts and deeply cleanse the skin.
I found on Youtube a great video that explains more about this topic and offers some good tips.