Why are more and more people using sun cream and the incidence of skin cancer increasing?


Skin cancer is one of the most common malignancies worldwide. Data released by the World Health Organization (WHO) show that in 2020 alone, more than 1.5 million new cases of skin cancer were detected globally, and more than 120,000 people died from this disease. In China, the incidence of skin cancer is increasing every year. The incidence rate of malignant melanoma (a type of skin cancer) increased from 0.31 cases per 100,000 people in 1990 to 1.19 cases per 100,000 people in 2019, a nearly three-fold increase in three decades.

Statistics show that approximately 65% of melanoma and 90% of non-melanoma skin cancers are directly related to UV exposure. Therefore, reducing UV exposure to the skin is one of the key strategies for preventing skin cancer. As a commonly used means of protection in our lives, sunscreen is used by an increasing number of people. However, since more and more people are using sunscreen, why is the incidence rate of skin cancer also increasing?

In July 2022, a team from the University of Toronto in Canada studied the connection between the incidence trend of melanoma and sun protection habits. They recruited 95 adults in Canada and asked them about their sun protection habits through online and offline group interviews.

The participants came from four Canadian provinces: Nova Scotia, Prince Edward Island, New Brunswick, and Newfoundland and Labrador. Among these 4 provinces, New Brunswick has a melanoma incidence rate that is on par with the Canadian national average, Newfoundland and Labrador has a below-average incidence rate, and the remaining 2 provinces have a melanoma incidence rate rate is higher than average.

Researchers found that although these residents live in different provinces, they all try to avoid outdoor activities at noon when the sun is shining, and they do not tan through sunbathing and other methods. However, their habits of using sunscreen and other sun protection measures were quite different.

Participants in Nova Scotia and Prince Edward Island, where melanoma rates remain high, generally reported more regular sunscreen use. For example, one participant said that he keeps a sample of sunscreen in his bag in case he needs it when going to the beach. They also wear sun protective clothing, hats and sunglasses. Residents of New Brunswick, which has the next highest incidence rate, also use sunscreen proactively and consistently, even for short periods of time outdoors. Likewise, they will insist on physical sun protection.

However, in Newfoundland and Labrador, which has the lowest rates of melanoma, participants had very different attitudes toward sun protection. They disdain sunglasses, have a deep-seated aversion to wearing hats, and prefer long-sleeved clothing. As for the use of sunscreen, it all depends on whether their current activities will directly expose them to the hot sun.

It can be seen that the more areas with high incidence of melanoma, the more people are aware of the health risks of sunburn and tanning. But strangely, while participants in Nova Scotia, Prince Edward Island and New Brunswick were very sun-conscious, they also talked about their sunburn experiences more frequently in group discussions, with many talking about My own painful experience of skin blistering and peeling after sunburn.

The researchers believe this exemplifies the "sunscreen paradox," a phenomenon known since the 1990s, in which people who are more aware of the risks of UV exposure and take protective measures will also be more likely to They are also exposed to the sun for longer periods of time, which in turn makes them more susceptible to sunburn. These "sun protection experts" think that they have taken good sun protection measures, and they have a false sense of security. However, many research data show that most consumers do not use enough sunscreen.

According to the U.S. Food and Drug Administration (FDA), when testing a sunscreen product for sun protection factor (SPF), 2 milligrams of the product should be applied per square centimeter of area. At the same time, the FDA recommends that consumers should apply this amount when using sunscreen. However, a recent large-scale questionnaire survey among Americans showed that consumers generally apply less than the recommended amount. The average application thickness on the face and body is 3 mg/cm2 and 1.52 mg/cm2 respectively, and the medians are 3 mg/cm2 and 1.52 mg/cm2 respectively. 1.78 mg/cm2 and 1.35 mg/cm2.

If the recommended application thickness of sunscreen is not reached, the SPF value will be greatly reduced. Some studies show that if you apply a sunscreen with an SPF of 16 at a thickness of 1 mg/cm2, the SPF will drop to 4, and if you apply it at a thickness of 0.5 mg/cm2, the SPF will drop directly to 2. In addition, the technique of applying sunscreen is also critical. Rubbing sunscreen instead of applying it gently can cause SPF to drop by up to 20%. In other words, although we apply sunscreen, it is likely that we do not apply it enough or use the wrong technique, and we do not achieve the sunscreen effect advertised by the product.

Of course, personal sun protection habits are not the only factor that affects UV exposure. Various factors such as cultural background, occupation and geographical environment also play a role. Studies have found that the global incidence of melanoma is inversely related to geographic latitude - the higher the latitude, the lower the incidence. In this Canadian study, the province of Newfoundland and Labrador, which has a lower incidence of melanoma, is also located at a higher latitude. The average summer temperature here is only 8 to 16°C, with fewer sunny days and frequent rain and fog. Nova Scotia and Prince Edward Island, on the other hand, have more sunny days, higher summer temperatures (14-18°C), and beach activities are more common.

So, how can we scientifically protect ourselves from the sun?

The American Academy of Dermatology (AAD) recommends that when choosing sunscreen products, priority should be given to broad-spectrum sunscreens that can block both mid- and long-wave ultraviolet rays (UVA and UVB), and ensure that they have an SPF value of no less than 30 and are waterproof characteristic. In daily use, whether it is hot summer or cold winter, whether the weather is sunny or gloomy, as long as we need to go out, we should apply sunscreen evenly to the exposed parts of the body 15 minutes before going out, including the insteps, neck, and Often neglected areas like ears and forehead.

Also, don’t skimp on using sunscreen. According to estimates, an adult needs about 28 grams of sunscreen to apply to the entire body. At the same time, don’t forget to protect your lips and use sunscreen lip balm with SPF no less than 30. After going out for activities, you need to reapply sunscreen every 2 hours. If you sweat after swimming or strenuous exercise, you should reapply it immediately.

In addition to applying sunscreen, other protective measures should be taken. Avoid direct exposure to the sun at noon if possible, wear clothing with an Ultraviolet Protection Factor (UPF) label, choose long-sleeved shirts and pants, and wear a sun hat and sunglasses for extra protection. Pay special attention to environments such as water, snow, and beaches that reflect sunlight and increase the risk of sunburn. Be extra careful in these environments.