Normally skin may need to be cleansed 2-3 times in the course of the day. Oilyskin types & individuals exposed to frequent & excessive pollutants may need to clean their skin as often as 4-5 times a day to wash away the grime and dirt.

well I agree what Swapnil has said, It is really important to keep your skin clean specially in such pollution. skin get torn'd out earlier and gets deposited leading to problems like black heads and pimples, specially on oily skin types. so a good body scrub should be used in order to remove dead skin cells and dirt from the skin to let the new skin breath for a glowing skin.