Spots are one of the many results of excess oil getting trapped in the pores. Some of the varieties are pustules or papules.
Inside the pore are sebaceous glands which produce sebum. When the outer layers of skin shed (as they do continuously), the dead skin cells left behind become ‘glued’ together by the sebum. This causes the blockage in the pore, especially when the skin becomes thicker at puberty. The sebaceous glands produce more sebum which builds up behind the blockage, and this sebum harbours various bacteria including the species Propionibacterium acnes, causing infection and inflammation.