Skin should be prepped prior to peels. There are several important reasons for this. One, it helps take off the stratum cornium (the dead skin layer) and allows the peel to penetrate deeper. Second, it reduces the hyperactive pigment cells that can cause post inflammatory hyperpigmentation ( dark spots). Third, it helps to see how compliant the patient will be with their skin care, in the critical and vulnerable post peel period.
I like to use a product with Retin A, hydroquinone, Kojic acid, hydrocortisone, Vitamin E and C, for a minimum of six to eight weeks, and even longer in darker skin types, before peeling my patients.
People with darker skin, or genetic background of darker skin, even if they are light skinned, have a greater risk of post inflammatory hyperpigmentation. Prep well before your peel. If you develop post inflammatory hyperpigmentation, have your doctor start you on a lightening program. See them frequently. Be patient as it may take a while to improve.