The consistent efficacy of daylight photodynamic therapy (DPDT) for the treatment of actinic keratosis (AK) found support in a study data published in Photodermatology, Photoimmunology & Photomedicine. In a study that assessed the relationship between DPDT efficacy and weather conditions, DPDT appeared to produce results comparable to conventional photodynamic therapy independent of seasonal weather quality. These results emphasize the efficacy and convenience of DPDT for the treatment of AK.

Prior research indicates that DPDT is comparably effective to conventional PDT for the treatment of AK and is substantially less painful. However, because DPDT requires exposure to sunlight, its suitability is dependent on weather conditions. Although research suggests that DPDT can be successfully undertaken even on overcast days, the precise effect of weather conditions on DPDT efficacy remains unclear. To better inform this gap, investigators at a dermatology center in Scotland compared DPDT treatment outcome data from the years 2016, 2017, and 2018. All DPDT treatment sessions were conducted during the spring and summer months (April through September). Weather data for the given months in 2016 to 2018 were collected from the National Weather Service of the United Kingdom. Metrics of interest included median daily temperatures, number of sunshine hours, and rainfall levels. Patient outcomes after 3 months of DPDT were compared across treatment years.

The total number of patients treated in 2016, 2017, and 2018 were 31, 34, and 65, respectively; the total number of treatment sessions were 71, 64, and 142. Compared with 2016 and 2017, 2018 had significantly less rainfall and many more sunshine hours. These conditions allowed the clinic to treat more patients in 2018 compared with 2016 and2017. However, mean patient response at 3 months post-treatment was comparable across all years. Specifically, the percentages of patients achieving “excellent” response in 2016, 2017, and 2018 were 31%, 32%, and 30%, respectively. Similarly, “moderate” or “good” response was achieved by 63% in 2018, 59% in 2017, and 69% in 2016. Mean daylight exposure time was also comparable across years. As such, investigators concluded that although weather conditions may affect the number of treated patients, the quality of DPDT is unhindered by weather. It remains important, however, that clinicians appropriately plan DPDT sessions to capitalize on clear weather.

Continue Reading

“[Our study] indicates that, with good treatment planning, DPDT is an effective, well-tolerated, convenient treatment for patients with field-change AK, irrespective of the quality of the British summer weather,” study authors wrote.

Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.


Kotb I, Lesar A, O’Mahoney P, Eadie E, Ibbotson SH. Daylight photodynamic therapy for actinic keratosis: is it affected by the British weather? Photodermatol Photoimmunol Photomed. 2021;37(2):157-158.