Spots are, generally speaking, a build up of grease or sebum in the pores. Generally sebum is a good thing but like in life, too much of a good thing and it all goes wrong!
Whiteheads are caused by a bacterial infection of the blocked pore which makes it inflamed and full of pus, blackheads are just blocked pores, which is why the product of a blackhead is generally hard. Euw!!!
