How come doctors say not to pop whiteheads?

I have found it really effective way of getting rid of nasty whiteheads. Usually the next day from popping them they are gone.





I know they say that it only spreads the oil and bacteria but usually nothing happens after I pop a zit. So should I continue popping them or not? Just curious.How come doctors say not to pop whiteheads?
Sometimes they can leave a slight scare on the face. (Mark)





so some Recomend not to pop them aspecially if they are still small.