A heat wave is sweeping across the Korean Peninsula. The ultraviolet rays from sunlight can cause skin cancer and skin aging, so caution is advised. Experts say that sunscreen is the most effective means to prevent skin cancer. It is recommended to apply sunscreen every 2 hours.
Alan Geller, a professor at Harvard T.H. Chan School of Public Health, noted in an interview with the Harvard Gazette on the 3rd that "applying sunscreen reduces the likelihood of developing skin cancer."
He introduced an Australian sunscreen study. Australia is a country with a high number of melanoma skin cancer cases. Melanoma occurs when there are issues with melanocyte cells, which can lead to malignant tumors and, in severe cases, death. It is categorized into primary melanoma, which does not infiltrate beyond the epidermis, and invasive melanoma, which penetrates the epidermis and metastasizes to other areas.
In the study in Australia, 1,600 individuals at high risk for melanoma applied sunscreen daily or applied it at their discretion. After 10 years, the group that applied sunscreen daily had 11 cases of primary melanoma and 3 cases of invasive melanoma. The discretionary group had 22 cases of primary melanoma and 11 cases of invasive melanoma. This implies that applying sunscreen daily can increase skin cancer prevention effectiveness by 2 to 4 times.
In the Australian study, SPF 15 sunscreen was used. SPF is an indicator of how much ultraviolet rays are blocked; the higher the number, the greater the UV blocking effect. SPF 15 blocks 93% of ultraviolet B rays, which cause skin inflammation, burns, and skin cancer.
Experts typically recommend sunscreen with an SPF of 30 or higher. Professor Geller stated, "SPF 30 has a UV blocking effect of 97%, while SPF 50 has 98%," adding that "there is no sunscreen that offers 100% blocking effect." Professor Kim Beom-jun of Chung-Ang University Hospital's dermatology department said, "In daily life, using SPF 30 sunscreen is sufficient for UV protection," and advised that "when engaging in activities that cause excessive sweating, like cycling or playing tennis in hot sunlight, SPF 50 is preferable."
Sunscreens typically fall into two categories: organic (chemical) sunscreens and inorganic (physical) sunscreens. Organic sunscreens absorb the UV rays into the skin and release them as heat. Inorganic sunscreens create a thin barrier on the skin that physically deflects ultraviolet rays. Organic sunscreens contain ingredients like oxybenzone and octinoxate, whereas inorganic sunscreens contain titanium dioxide and zinc oxide.
Professor Geller noted that "experts recommend physical sunscreens." Professor Kim added that "while organic sunscreens are easy to apply, ingredients like oxybenzone and octinoxate have detrimental effects on coral and marine ecosystems," suggesting that "it is better to use inorganic sunscreen when swimming in the ocean for the sake of the environment."
Sunscreens are available in various forms, including cream, gel, stick, and spray. Creams and gels can be applied to the face by hand. Sticks and sprays can be rubbed or sprayed on the face without direct contact with the hands. Individuals should choose formulations that suit their skin condition. Professor Geller stated, "It is difficult to guarantee that spray sunscreen is applied sufficiently to protect all exposed areas of the body."
Experts recommend reapplying sunscreen at least every 2 hours. Professor Geller stated, "When sweating or swimming, sunscreen should be reapplied every 80 minutes," and emphasized that "sunscreen should be applied to all areas, including the tops of the feet, neck, ears, and scalp that are not covered by clothing." One-third of male melanoma patients develop tumors on their backs, while one-fifth of female patients have tumors on the back of their legs.
Some individuals believe they only need to apply sunscreen when the sun is hot. Professor Geller advised that "sunscreen should also be applied on cloudy days." He also recommended checking whether the sunscreen is water-resistant and whether it has not exceeded its expiration date.