Large pores on the nose are the result of large productions of sebum from the sebaceous glands in the nose, squeezing blackheads and pimples from the nose, and even from aging and sun damage.
Many treatments for enlarged pores only help by cleaning out the pores and drying out and reducing some of the oil production from the skin, but they can never permanantly reduce the pore size.
The pores on your nose are there because they release skin oils that keep your skin lubricated and keep your skin from dehydrating.
Excessive sebum production in the nose can promote bacteria growth that in turn clogs the pores and causes blackheads. Once the pores are enlarged, aging and sun damage can worsen the effects because of less collagen production.
Cleansing and exfoliating the problem areas of the nose daily can assist in reducing the size of the enlarged pore. Laser treatments can provide a longer lasting and more effective treatment.
Even with treatments from cleansing, facials or even lasers, the enlargement of pores can happen again.