Just as any brightening regimen must be approached with diligence to experience results, daily use of sun protection is just as imperative. 

Even the strictest of brightening regimens can be counteracted by minimal exposure to UV light. When a hyperpigmented area is exposed to UV light, more melanin production is triggered on a cellular level, causing further darkening. Ironically, this production of melanin is just your skin trying to protect itself from damaging UV light. 

Daily application of SPF will help shield skin from UV light to control melanin production on a cellular level.  It can even help lessen the appearance of hyperpigmentation triggered by hormone fluctuations (such as melasma) or post-inflammatory hyperpigmentation (scarring).