Our skin is covered with tiny hairs many of which we cannot see. Each hair follicle has a sebaceous gland attached to it which produces oils (sebum). These oils often get trapped in the pores due to an accumulation of dead skin cells on the surface. The trapped oils will then stretch the pores until they become visible to the naked eye.
Oil and UV light will exacerbate pigmentation, whereas oil and dirt will lead to blackheads and whiteheads which then lead onto spots. Pore size can be much improved with ZO skincare, HydraFacial and chemical peels.