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Background/Objectives Solar (actinic) keratosis (AK) is an emergent concern worldwide and is associated with an increased risk of development of non-melanoma skin cancer, especially squamous cell carcinoma. Daylight-mediated photodynamic therapy (DL-PDT) using methyl aminolaevulinate cream has proved to be an effective, nearly painless, and more convenient alternative to conventional PDT for the treatment of AK. In a phase III, randomised, controlled trial performed in Australia, the mean irradiance (light intensity) received by patients during DL-PDT treatment, assessed via a spectroradiometer, was 305 W/m2 (min. 40 to max. 585 W/m2) with similar efficacy irrespective of intensity or dose. The objective of the present meteorological study was to assess the suitability of natural daylight to perform DL-PDT for the treatment of face and scalp AK during different periods of the year and different geographical locations and latitudes across Australia. Methods To determine daylight irradiance during a complete year in eight different geographical locations throughout Australia, we used meteorological software (Meteonorm, Meteotest, Bern, Switzerland), and available solar radiation and weather data from 1986–2005. Results The average daily irradiance remained within the levels (40–585 W/m2) measured during the clinical DL-PDT study in Australia, throughout the year and in all geographical locations investigated (yearly average from Darwin 548 W/m2 to Hobart 366 W/m2). Conclusions DL-PDT for the treatment of face and scalp AK in Australia can be performed effectively throughout the entire year as long as weather conditions permit daylight exposure and allow participants to remain under direct light for 2 h.

Hidradenitis suppurativa (HS) and pilonidal cysts are chronic, inflammatory skin conditions involving apocrine gland-bearing skin. Treatment is limited and unsatisfactory. Photodynamic therapy (PDT) has been reported to be safe and effective in the treatment of several off-label skin conditions. We report the case of a 29-year-old man affected by HS and pilonidal cysts since the age of 21. In the past, the patient was treated with antibiotics, corticosteroids and retinoids, without significant clinical improvement. Treatment with methyl aminolaevulinate (MAL)-PDT was started. A topical MAL cream (Metvix) was applied to the affected areas with an occlusive dressing for 3 h and irradiated with a red light source. Therapy was repeated every 15 days for a total of nine applications. The patient completed a 6-month follow-up and achieved an almost complete clinical remission of the skin lesions (80%) and complete resolution of the itching and discomfort. This is the first case of HS associated with pilonidal cysts treated with MAL-PDT. MAL-PDT was effective and well tolerated in our patient. The costs of this therapy represent an important limitation, taking into account the high number of sessions that were performed compared with non-melanoma skin cancers.