Cleaning the skin is important as it removes the dead cells from the surface of the skin. It also will remove dust and dirt that may clog the pores on the skin. If the dust is allowed to accumulate, it can block the pores thus blocking the secretion of sebum. Sebum mixes with other lipids and sweat and forms a coating on the skin called acid mantle. Acid mantle protects the skin against bacteria and keeps the skin hydrated.