The first step to take towards treating tanned skin is using a broad-spectrum sunscreen consistently. Please ask your dermatologist to prescribe you one as market sunscreen may often not be enough. Next, your doctor may add on topical creams and serums with lightening ingredients like glycolic acid, kojic acid, Vitamin C etc. For severe tan, procedures may be suggested. Chemical peels with lightening agents like glycolic acid, TCA, salicylic acid etc. taken regularly for a few sessions can help. For more severe cases, Q-switched Nd:YAG laser can effectively get rid of pigmentation deep under the skin and improve skin quality at the same time. Time taken for results may be several months and treatments are often combined together.