What causes dirty skin and is there any cure for it?

Skin becomes dirty when exposed to sun, pollution etc...

And what do u exactly mean by dirty...

Our skin generates new cells each day and discards the old ones, also skin is the largest organ meant to protect inner organs of our body

So it is very much necessary to keep skin clean and healthy

Scrubbing should be used to remove dead cells

There are also lots of cleansers and face washes available, choose one according to your skin

Make sure skin is not exposed to extreme climats
And yeah drink lots of water and eat right...

Are you specifically inquiring about dirty skin related to acne problems? If so, acne is hormonal although your eating habits, cleaning habits, etc have a role in the health of your skin, hormones play an even bigger role. Dirty skin doesn't equate acne. Clogged pores, an overproduction of oil, and blackheads are all caused by a hormonal imbalance.