Nowsebumisanoilysubstancethatusuallymovesupandoutoftheporesandlubricatesyourhairandskinbutsometimesyoucanproducetoomuchsebum, whichcreates a trafficjamforoilandbacteriaunderthesurface.
Now, itcantakedaysorevenweeksforthatbacteriatotriggeraninfectionthateventuallymakesitswaytothesurfacebutonceitdoesandyouget a pustule.