This study looks at the safety and how well a treatment works for actinic keratosis (AK), which are rough, scaly patches on the skin caused by sun damage. The treatment uses a special gel called **Ameluz®** combined with a red light lamp called **RhodoLED** to improve these skin areas. Participants must be 18 years or older and have 4 to 15 mild to moderate AK spots on their arms, legs, neck, or trunk. The study lasts about 12 weeks, during which participants will receive up to two sessions of photodynamic therapy (PDT). **Key Points:** - **Duration:** The study will take about 12 weeks with up to two PDT sessions. - **Eligibility:** Participants need to be in good general health and avoid sunbathing or tanning beds. - **Risks:** People with allergies to the gel or certain medical conditions, like unstable cardiovascular disease, cannot join. Before starting, participants must sign a consent form and provide health information. Women with childbearing potential must have a negative pregnancy test and use effective contraception during the study. Participants should avoid moisturizers and topical treatments on the test area for 24 hours before visits.