Group 1 - The core viewpoint of the articles emphasizes the importance of proper storage and usage of sunscreen products to maintain their effectiveness, countering the myth that opened sunscreen loses its protective ability even within its expiration date [1][2][3] Group 2 - Sunscreen products can be categorized into two types: those containing physical blockers (like zinc oxide and titanium dioxide) which are stable and maintain effectiveness even after opening, and those with chemical blockers (like avobenzone) which are less stable and require careful storage [1] - Proper storage conditions for sunscreen include avoiding direct sunlight and high temperatures, keeping the product dry and sealed, and minimizing transfer to other containers to prevent contamination [2] - Indicators of sunscreen expiration include visible separation, clumping, discoloration, or unusual odors, and a decrease in effectiveness can be tested by observing skin reactions after application [2][3] Group 3 - Effective application of sunscreen requires using an adequate amount, typically the size of a one-yuan coin for facial coverage, and applying it 15 to 30 minutes before sun exposure [2] - Reapplication is recommended every 2 to 3 hours during prolonged sun exposure to ensure continued protection [2] - Sunscreen should also be applied to all exposed skin areas, and physical barriers like hats and umbrellas can enhance protection [3] - It is important to cleanse the skin of sunscreen after sun exposure, using appropriate cleansing products [3]