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Skin is a constantly regenerating photosensitive organ and the under eye area is even more sensitive.
Suntan is best prevented by sunscreen than treated .this is because the darkening of skin is due to a pigment melanin
deposited in the skin and it cannot be removed or erased off the skin . But with time as our skin is renewed the pigmentation decreases and so our tan decreases.
So please do not try any drastic methods to erase a tan.
There are many creams in market but many have sideeffects too so it is best to consult a dermatologist
if you really are in a haste to get rid off it.you may try natural alovera too.