Tan is not due to pollution. When ultra violet UV rays from sunlight strike the skin which is exposed to sunlight , then melanin is produced in the skin. This melanin pigment of skin when in excess is called as tan. It is actually a protective mechanism provided by nature to us. Melanin pigment forms a layer and prevents entry of UV rays deeper into skin. But since it causes darkening of skin we dont like it. It is best to wear clothes which cover exposed areas of body. Extra protection can be obtained with sunscreen usage in copious amounts repeatedly. But there are many conditions like cutaneous macular amyloidosis or post inflammatory hyperpigmentation.. etc .. so please show to a dermatologist before taking a treatment cream.