Everything about sunscreen: The common belief that scientists say is completely wrong

On hot summer days, sunscreen for most of us is an essential device when leaving home, but there are many misconceptions about it. These beliefs are often promoted by health influencers that introduce alternatives for sunscreen. Some of these beliefs are shared than more prestigious sources, and some have become popular over time. What does SPF really mean? Does the only UVA rays cause aging? And do the sunscreen really become “active” 5 minutes after use? Here’s a look at what the leading research and experts say about these beliefs.

First, the SPF 50 does not mean that you can stay in the sun 5 times more than when you are not sunscreen. The higher the SPF, the greater the protection, but this number is different from what many people think. The US Food and Drug Administration (FDA) points out that SPF does not tell you how much you can stay in the sun without sunburn. For example, this does not mean that if you usually get a sunburn at an hour and use the SPF 8 sunscreen, it will take eight hours to get sunburn.

Rather, SPF is a ratio. The ratio of ultraviolet radiation (UV) that, despite the sunscreen, causes sunburn, to the amount of ultraviolet that causes sunburn without sunscreen. This generally shows the percentage of sunburn rays that continue to pass through the sunscreen. For example, a sunscreen with SPF 25 allows a twenty -fifth (1 %) of the sun’s beams, while SPF 50 allows a fifty (1 %) passage. In other words, SPF 25 blocks about 1 % and SPF 50 blocks about 2 % of the UV beam. The important point is that these calculations are based on laboratory experiments, in which the sunscreen is much more (1 mg per square cm) of what most people use.

So most of us are exposed to UV more than these numbers. In any case, for sunscreen effectiveness, it must be renewed regularly during the day (at least every two hours, as well as after swimming or sweating). For the best protection, look for sunscreen with high SPF and with “wide range” protection. In the UK, there is a UVA Star Rating system that shows the effectiveness of sunscreen against high -wave UVA beams, and the number five is the highest level of protection.

Does UVB only cause sunburn and UVA only aging?

That UVA only causes aging and UVB not only sunburn. Both types of rays can cause cancer. Ultraviolet light can be divided into smaller bands of different wavelengths. The UVA has a longer wavelength that can penetrate more deep than the skin, while the UVB waves are slightly shorter and only penetrate the outer layers of the skin. However, this does not mean that UVB does not cause deeper damage. It has long been thought that UVB was a major cause of skin cancer, but research has shown that UVA damage may also be involved in skin cancers.

These findings lead to the production of sunscreen formulations that block both types of UV beams. Anthony Young, an retired experimental footbalt at King London College, says skin cells respond by releaseing intermediaries such as cytokines, which cause deeper layers and help long -term injuries, aging and cancer. Mary Samarlad, a dermatologist in London and a spokesman for the British Dermatology Foundation, says both UVB and UVA are involved in aging and tanning. He adds to patients who have conditions such as melasma (dark spots on the skin) that they should also protect themselves against a wide UV spectrum, including UVA, because UVA darkens the skin.

Why can you be sunburnt on cloudy days?

Many of us put the hats and sunscreen while seeing the cloud, but that can be a wrong decision. The reason is that although clouds scatter the sun’s rays, their effect on the amount of UV beam on Earth may be very different. Very thick clouds can reduce about 2 % of the UV beam that reaches the surface, but thinner or scattered clouds may have no effect. Even some types of clouds can cause more UV beams in some places than a sunny day.

Fourth, not all shadows are the same. When it comes to protecting the sun, what matters most is UV Index, a criterion of UV beam level that public health organizations recommend people to use like temperatures to plan their day. When the UV index is three or more, public health organizations recommend wearing hats, protective clothing and sunscreen and looking for shade. But experts warn that the type of shadow is important. Brian Difie, a retired professor of skin science at the University of Newcastle and the inventor of the UVA star rating system, says the coastal umbrella that is usually a few meters above your head exposes your skin to almost all open sky and provides only a SPF 5 protection.

For example, one experiment showed that while 5 % of people who used sunscreen suffered from sunburn, 5 % of people who only used a coastal umbrella had sunburn. Other types of shade that provide little protection include the porch ceiling (if it still receives sunlight) or an indoor place. Leaf trees may provide more protection. For example, a dense oak tree can provide a SPF 20 protection, but many types of trees may provide only SPF 5 or less. In general, the more space is covered by a canopy or the closer the crown of dense trees and the closer the trees, the more protection. The UV beam can also be reflected from surfaces such as glass, sand, concrete and water. Therefore, watch the reflected UV beam.

Use of sunscreen all year: Is it necessary?

You may not need to use sunscreen throughout the year, but it depends on your place of residence and work. In general, even for people with light skin sensitive to the sun, according to the World Health Organization, when the UV index is below two, the risk of damage caused by UV is limited and additional protective measures are not required. This means that in some parts of the world, most people do not need to use sunscreen throughout the year. For example, Difie says the UV index is less than three from mid -October to mid -March. For people who spend most of the day indoors, exposure to UV on a winter day is less than a minute compared to the time they are sunny.

Difie says about using the winter sunscreen that if you are in the office and gets the air and rain and December, the use of sunscreen is meaningless. He adds that it has no profit for you. Of course, this also has its own conditions. Studies have shown that in some cases snow covering can increase UV beam by up to 1 %. So if it’s winter but you are skiing all day, protecting the skin from sunlight is important. Samarid also points out that the UV index can change rapidly. He says that if you are out and the clouds suddenly go away and you are not protected, you may have sunburn. In other words, on a summer day, you probably trust the UV index less on a summer day until the UV index is constantly low, such as mid -winter.

Should the mineral sunscreen be visible?

The belief that mineral sunscreen only works when visible is incorrect. Although mineral sunscreen leaves a white layer on the skin due to the reflection of the visible light spectrum, this does not indicate their effectiveness in protecting the skin against UVA or UVB. These beams are only UVR spectra on the ground and cause damage and skin cancer. Also, since mineral sunscreen first works with UV beam absorption and reflects or scatters only 2 % of UV beams, there is no reason to look “reflectable” to work.

Does sunscreen cause vitamin D deficiency?

Regular use of sunscreen may not cause vitamin D deficiency. Although our body produces a hormone called vitamin D3 by exposure to UVB from sunlight, this does not mean that using sunscreen makes a big difference. Few people are sustainable enough, so most of us are more exposed to UV than we think. For people with light skin that lie on a sunny summer day, it is often enough for only a few minutes to expose the sun (depending on factors such as UV index and the amount of skin exposed) to maximize the production of vitamin D3.

However, under other conditions, such as walking in a full -fledged urban environment, this may be closer to about an hour. However, after reaching that level, increased sun exposure does not mean increased vitamin D. Instead, DNA damage increases, but vitamin D3 reserves remain constant. This is probably because past research has shown that people who use sunscreen are more likely to be deficient in vitamin D than those who do not use. However, Difie points out that most of the research has been carried out in sunny countries with relatively low SPFs.

Should it be sunscreen 5 minutes before the sun?

The sunscreen does not take 5 minutes to “activate”. Most sunscreen stickers say that it should be used 2 to 5 minutes before sun exposure, but that does not mean that the sunscreen is ineffective during this period. In fact, studies have shown that sunscreen can be effective immediately and many manufacturers confirm this. Michelle Wang, a chemist and author of the book Beauty, which often deals with misconceptions about sunscreen in the online space, says it gives enough time into a uniform “layer” that is more difficult to spread, sweat or wash. 5 minutes may be a conservative estimate of the time the process takes. A small study found that the test sunscreen created this layer only after eight minutes. However, following the manufacturer’s instructions is always better.

Don’t people with dark skin need sunscreen?

The belief that people with dark skin do not need to worry about UV beam is incorrect. Melanin in darker skin provides some natural protection against UV, which is why the prevalence of melanoma in black populations is much less than those with light skin. However, people with darker skin can also develop sunburn and skin cancer, and exposure to sunshine can cause hyperpigmentation disorders such as melasma. For this reason, dermatologists such as Samarhad recommend that people with any skin color use sun protection.

Does sunscreen increase skin cancer rates?

Melanoma rates are rising among people with light skin in countries such as the United States, Britain and Australia, but that does not mean that sunscreen is the reason. On the one hand, cancers are greater among the older populations, and the population in these countries is getting older. We also know that the more sunburn or the use of tanning beds, the greater the risk of skin cancer, and both have been very popular in recent decades. A study on skin cancers in Australia found that about two -thirds of melanomas and almost all basic and stone cancers were specifically caused by UV exposure. While a study of all patients diagnosed in Sweden with melanoma between the ages of 1 and 2, it showed that melanoma was likely to have been in the upper body and organs under the age of five, indicating that exposure to UV was a major cause.

Samarid says if you care about your health and want to keep your life and health, protecting yourself from sunburn is one of the best things you can do. But experts point out that there is an indirect way that sunscreen may increase skin cancer. This is an unstable feeling. Difie says when people are suiciments, they think they have an invisible barrier to the sun and tend to change their behavior and spend more time under sunlight. But he does not believe that the sunscreen themselves are carcinogenic.