You seem to be having this darkness due to sun burns. Use a sunscreen of SPF 30 everyday. Keep the face well moisturised. If the lesions over face are too red, dry or itchy, you might use mild steroid
cream for few days. Let the skin come to its normal texture. Once the dryness has gone, to treat tanning
you may undergo sessions of chemical peels
. You may also use a Glycolic acid
or hydro quinone based cream to reduce darkness.
Hope that answers your query. Take care.