Inclusion Criteria 
1. Patient is 18-80 years of age? 
2. Patient received a transplant greater than 6 months ago and is taking immunosuppressive therapy? 
3. Patient was given a diagnosis of actinic keratosis in the past year and/or has had a history of 1 actinic keratosis at 5 or more visits over the past 10 years? 
4. Does the patient use a compatible smartphone? (Apple version = 7, Android version = 4.4.2) 
5. Is patient willing to commit to dermatology visits (including standard of care visits) every three months for one year? 

If any of the above answers are “no”, the subject does not qualify for this study. 

   Exclusion Criteria 

1. Has the patient received UV therapy in the past year? 
2. Is the patient’s work/lifestyle incompatible with wearing a UV sensor over the course of 1 year (i.e., construction, lifeguard)? 
3. Will the patient have difficulty controlling UV exposure (i.e. live in nursing home, extended hospitalizations)? 
4. Does the patient have 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? 
5. Has the patient 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 12 months? 
6. Is the patient an employee or direct relative of an employee of the investigational site or study sponsor? 

If any of the above answers are “yes”, the subject does not qualify for this study.