When the season of strong sunlight arrives, many people reach for sunscreen that has been sitting in a drawer. If the product is left over from a purchase last year, there is something that must be checked before applying it: the period of use after opening.
According to the medical community on Wednesday, unopened sunscreen can be used for two to three years from the date of manufacture, but the standard changes once it has been opened. The number "6M" or "12M" written next to the small jar-shaped icon on the back of the container indicates the period of use after opening. These mean six months and 12 months, respectively, and once this period passes, the ultraviolet-blocking ingredients break down, making it difficult to achieve the expected level of protection. Dr. Nora Zafar, a British dermatologist, recommended through the British outlet Express that people write the date directly on the cap or container when first opening it.
Whether sunscreen has deteriorated can also be checked with the naked eye. Inorganic sunscreen products develop grains or a coarse texture, making them difficult to spread evenly on the skin. Organic sunscreen products tend to turn yellowish or become watery as oxidation progresses. The Cleveland Clinic in the United States recommends against using products that show such changes, even if the indicated expiration period remains. In particular, ingredient breakdown accelerates when products are stored for long periods in high-temperature environments, such as inside cars or in places exposed to direct sunlight. Sunscreen should be stored in a cool, dry place, and the cap should be closed after use to minimize air exposure.
Properly storing sunscreen and using it within its period of use matters because ultraviolet exposure is directly linked to skin cancer. According to the Health Insurance Review and Assessment Service, the number of skin cancer patients in Korea increased more than 30% over four years, from approximately 20,300 in 2018 to 31,000 in 2022. Based on the patient growth rate over the past five years, skin cancer ranked second after prostate cancer. About 90% of non-melanoma skin cancers are associated with exposure to solar ultraviolet rays, and research has found that daily use of sunscreen with SPF 15 or higher, as directed, lowers the risk of developing squamous cell carcinoma by about 40%.
Applying sunscreen correctly is also important. The Korean Dermatological Association recommends applying it 20 to 30 minutes before going out and reapplying every two to three hours during outdoor activities. It is advisable to apply more frequently when sweating heavily or after water activities. The Ministry of Food and Drug Safety also advises that the key is to apply a sufficient amount evenly, rather than relying on SPF and PA ratings alone. No matter how high the rating of a product, the blocking effect decreases if an adequate amount is not applied or if it is not reapplied. It should be applied thoroughly not only to the face but to all exposed areas, including the neck, ears and backs of the hands, and scalp protection should also be considered if the scalp is exposed.
Experts explain that when used in the recommended amount daily, it is common to use up a bottle within a few weeks to two months. If a product opened last year still has a lot left, it can be seen as a sign of insufficient use frequency. Ultraviolet rays affect the skin even on cloudy days or indoors. Making sunscreen a daily habit regardless of the season is the basis of skin cancer prevention.
