Besides heredity, there are two main causes- internal cause and external cause.
-Internal cause1: The sebaceous is over active.
Affected by hormones in puberty, the sebaceous gland becomes active and the grease secrete exuberantly, making the pores large.
-Internal cause 2: The skin is natural aging.
As your age frows, your skin's resilience will decrease inevitably, thus is becomes large.
-Internal cause 3: The skin cells lack water.
As cells are aging, the moisture will lose quickly. Cells become wizened, making the cell speaces bigger, then the pores become larger.
-Internal cause 4: The metabolism of keratin is slow.
Aging cells make the metabolish of keratin slow. The aging keratin will make pores clogged, so they become large.