Fifteen years ago the US Food and Drug Administration approved the use of photodynamic therapy (PDT) in dermatology for the treatment of actinic keratosis (AK). Photodynamic therapy using topical agents in combination with visible lighthasbeen investigatedextensively with a general consensus that in cutaneousoncology, PDT isprobablybest suited for treating patients with multiple or larger superficial lesions. In a meta-analysis, Patel et al1 concluded that PDT resulted in a 14%better probability of complete clearance of AK compared with cryotherapy. Additional potential benefits of PDT such as superior cosmesis and better patient acceptance havenotbeendemonstratedclearly.Althoughcryotherapyand PDT require the acquisition and use of specialized materials and equipment, only the former is typically a first-line approach for most practicing dermatologists. Notwithstanding the apparent superiority of PDT to cryotherapy, the light-based approach to treating AK has 3 major limitations.Thecurrent financial remunerationmodel is amajordisincentive, given thehigher costs forPDT in termsofpractitioner time and equipment comparedwith cryotherapy. AlthoughPDTappears tobea simple concept, inpracticeoptimal results may require longer drug incubation times and perhaps light-dose fractionation to generate a sufficient tissue effect. Clinicians aiming to streamline the treatment process by shortening the incubation times may achieve inferior results owing to insufficient in situ generation of local protoporphyrin IX and singlet oxygen. Finally, local pain owing to photosensitizer activationduring light exposure is perhaps themost striking adverse effect that clinicians need to anticipate and manageduringPDT.Somepatientsmayneverbewilling toundergo a second treatment after their first painful PDT experience. Patient education and assignment of designated staff to use specific analgesic techniques are highly recommended to manage patient discomfort during PDT. All 3 of these limiting factors necessitate added time and resources compared with the relatively brief outpatient visits for cryotherapy, inwhich liquidnitrogen is simply andefficiently dispensed to the skin. That PDT yields some cosmetic benefits to patients with photodamagedskin representsonemeansbywhichsomepractitioners areable tomake this serviceeconomically feasiblevia private remuneration.NeverthelessAK is still consideredapremalignant condition, the treatment ofwhich ismedically necessary. Alternate compensation or fundingmodels are needed to commit the proper resources to providing optimal PDT. The future of PDT may rest in the innovation of “daylight” PDT,whereby patients are exposed to ambient outdoor light right after the application of topical aminolevulinic acid or its congener. Although this method is an off-label application,daylightPDTobviates thenecessity fora specialized treatment lamp and appears to be a less painful experience for patients.2 Controlled trialswill beneeded to establish its clinical efficacy and utility clearly. Perhaps the most tantalizing irony of daylight PDT is the specter of treating a solarinduced neoplasmwith sunlight itself.