Validation of SHADE a Mobile Technology for Monitoring of Ultraviolet Exposure

Inclusion Criteria: * between 18-80 years of age * given a diagnosis of actinic keratosis in the past year and/or has had a history of \>5 actinic keratosis over the past 5 years * has a compatible smartphone ((Apple version \>= 7, Android version \>= 4.4.2; no Jitterbug or Samsung Galaxy J3) * willing to commit to dermatology visits (including standard of care visits) every 3 months for 6 months Exclusion Criteria: * received UV therapy within the past 6 months * work/lifestyle incompatible with wearing a UV sensor over the course of 1 year * has difficulty controlling UV exposure * has a medical condition judged incompatible with the study by the enrolling physician including the presence of an ICD or an existing plan for extended inpatient treatment * has received field therapy (i.e., entire face or scalp) for the treatment of actinic keratosis (i.e., topical imiquimod, 5-fluorouracil, photodynamic therapy) in the past 3 months * is an employee or direct relative of an employee of the investigational site or study sponsor