Twenty patients with multiple actinic keratosis on the face will be enrolled in the study and will be treated with Daylight Photodynamic therapy.

Before and after skin biopsies will be performed, for histological and immunohistochemical analysis.

Twenty patients with multiple thin actinic keratosis (AK) on the face will be included in the study. They will be informed of the procedure in detail and sign a consent form.

Digital photographs will be done in a standardized way. Prior to treatment, all patients will undergo 2 skin biopsies under local anesthesia and with a 2 mm punch biopsy. One biopsy will be done over an AK lesion and the other in an area with no apparent AK (field cancerization).

The patients will be treated with Daylight Photodynamic Therapy, following these steps:

1. mild curettage of the AK lesions
2. application of a chemical sunscreen with sun protection factor (SPF) 30
3. application of methyl Aminolevulinate cream (Metvix R, Galderma Laboratories)
4. exposition to daylight, for 120 minutes
5. cleaning of the face

Three months after treatment, two new skin biopsies will be collected, 1cm away from the initial biopsies. On the same date, new photographs will be made following the same standards as pre-treatment photographs.

Inclusion Criteria:

-multiple (at least five) actinic keratosis on the face, grades I and II

Exclusion Criteria:

• phototypes IV, V and VI
• patients treated for actinic keratosis up to 6 months before
• history of allergy to methyl aminolevulinate
• history of photoallergy
• pregnancy