Alan Geller, a senior lecturer at Harvard T.H. Chan School of Public Health, emphasizes the critical role of sunscreen in preventing skin cancer. A comprehensive Australian study spanning ten years and involving over 1,600 high-risk participants demonstrated that daily use of SPF 15 sunscreen reduced the occurrence of primary melanomas by half, decreasing cases from 22 to 11, and invasive cases from 11 to 3. He advises choosing a broad-spectrum, water-resistant sunscreen with an SPF of at least 30 and recommends reapplying it every two hours, or every 80 minutes if engaging in activities like swimming or sweating. Because most people use only 20–50% of the recommended amount, choosing products with a higher SPF can make up for this shortfall.Physical sunscreens with zinc or titanium are often preferred. Geller stresses the importance of applying about one ounce of sunscreen per use and making sure to cover often-missed areas such as the ears, feet, lips (using an SPF 30+ balm), and back. He also supports public health initiatives such as providing free sunscreen dispensers and suggests wearing sun-protective clothing, seeking shade, and being mindful of sun exposure.