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This summer in the Netherlands, sunscreen will be offered free of charge to the population, through dispensers located in city parks, sports areas, around hospitals and various other public places. Various municipalities have organized themselves as part of an initiative to raise awareness of the importance of protecting oneself from the harmful rays of the sun, which can cause numerous health problems starting with skin cancer. The Netherlands has seen a significant increase in cancer cases attributable to sun exposure in recent years, as have many other countries in Europe.
– Listen also: The special episode of “It takes a science” on sunscreens
The use of sunscreens is recommended by dermatologists not only because it allows you to avoid burns, but also because their correct use significantly reduces the risk of developing skin cancer. The problem is that few make a “correct use” of sunscreens, applying the right amount and repeating the applications several times during the day, as indicated on the packaging and above all in the guidelines of the World Health Organization and various other health institutions.
Skin
The skin is the most important protective barrier between our body and our surroundings. Throughout its life it is subjected to physical and chemical stress, including exposure to sunlight which can change its characteristics, for example making it dehydrated and reddened. Excessive and prolonged exposure to ultraviolet rays (UV), emitted by the Sun and which we cannot see with the naked eye, is among the most important risk factors in the onset of melanoma and other skin cancers.
UVA and UVB
In general, sunscreen is used to reduce the amount of ultraviolet rays that reach our skin. Most of the UVB rays are filtered by the atmospheric ozone layer, but the amount that reaches the ground is still sufficient to cause us some problems. They are the main culprits of sunburn and also for this reason they are the ones on which we had focused the longest in the past, while more clear research and data were emerging on the effects of another type of ultraviolet rays: UVA.
Unlike UVB, UVA has the ability to penetrate deep into the skin, stimulating the production of free radicals, extremely reactive atoms or molecules that interact with what they encounter, often creating damage. For example, they can deteriorate collagen, a very important substance for the skin, and accelerate its aging, or they can increase the risk of cancer.
UVB is usually shielded by glass, such as a car windshield, while UVA is not. Modern sunscreens protect against both UVA and UVB, but it’s always a good idea to check the label to ensure protection.
Tan
The skin darkens in the sun as a defense mechanism against ultraviolet rays. When we expose ourselves to sunlight, melanocytes are activated, specialized cells that produce melanin, a substance found in various tissues of our body including the skin.
The activation always takes place, even in the middle of winter, but the production of melanin increases when you are exposed to the sun for long periods. It is in this circumstance that the skin darkens and becomes tanned, but its coloring is in no way the same. indication of being “healthier”: it is simply a sign that the body has taken action to try and protect us from the sun’s rays. However, the ability to protect is very limited and derives from how you are made, that is, from your phototype.
Phototype
The main reference for determining the phototype was developed in the mid-seventies by Thomas B. Fitzpatrick of the Harvard School of Medicine in the United States. He formulated a classification scheme for human skin color based on the response of different people to UV. The system was then modified and integrated about ten years later and groups people into six categories: from phototype I which includes people who burn and do not tan, usually with light hair and eyes, to phototype VI in which including people who don’t get sunburned and have darker skin.
Ingredients
In the European Union, sunscreens are highly regulated, even though they are included in the large group of cosmetics (which have different rules from medicines, for example). There are 28 authorized sunscreens, i.e. the molecules that have the task of absorbing/reflecting UV rays: each sunscreen has an absorption and a reflection component, with proportions that vary according to the products and needs. Among the most common components is titanium dioxide, which makes up a quarter of the content of the sunscreen, to which the other filters are added: overall the creams are therefore very concentrated, even when it is not indicated on the label ( “focused” is one of those terms used a lot by marketing).
Sun Protection Factor – SPF
The number indicated on the packaging of sunscreens indicates the ability to protect the skin from the sun. It is determined experimentally with tests that are carried out on about twenty volunteers, whose back is exposed to a lamp that emits ultraviolet rays imitating those of the sun. One side of the back remains unprotected while the other is covered in sunscreen.
The lamp is calibrated to produce an amount of UV that causes erythema on each subject’s unprotected skin, then it is moved to the area with the sunscreen, gradually increasing the dose of UV rays. After a few hours, the differences between the various areas are evaluated and the ratio between the minimum dose of UV necessary to produce an erythema on skin protected by the cream and for skin without protection is calculated. Finally, the SPF, the number indicated on the packaging, derives from this calculation.
(Getty Images)
For example: if it takes fifty times more UV to cause erythema to develop on skin protected by the cream than on unprotected skin, this means that the cream has an SPF of 50.
The procedure is carried out for UVB, while for UVA the system is more complex and requires the use of other tests. The acronym UVA-PF followed by a number indicates the protection factor for these ultraviolet rays, but usually only the presence of UVB protection is indicated on the packaging. Manufacturers can only put it on creams if the UVA-PF in the cream is at least one third of the SPF, otherwise they can’t indicate anything on the label.
How much sunscreens protect
An SPF 10 lets through 1/10 of UVB, therefore stopping 90 percent, an SPF 20 lets through 1/20, therefore stopping 95 percent, and so on. These are the values that are usually found on the packaging and the relative percentage of effectiveness in blocking the sun’s rays:
SPF 10: 1/10 → 90%
SPF 20: 1/20 → 95%
SPF 30: 1/30 → 97%
SPF 50: 1/50 → 98%
SPF 100: 1/100 → 99%.
A “total” protection does not exist and in the case of the European Union, manufacturers are advised not to use numbers beyond the indication “50+”, precisely so as not to lead one to think that with the highest SPF number one has total protection . On several occasions there has also been discussion of eliminating the numerical indication and leaving a more generic one indicating low, medium, high and very high protection, but there are interests (above all commercial) in maintaining the numerical indication.
How much sunscreen should you wear
The SPF number gives the corresponding protection only if the sunscreen is used correctly, applying the right amount, i.e. 2 milligrams for every square centimeter of skin: using less of it significantly reduces the protective effect. You need more or less 30 grams of cream for the whole body, about one sixth of a normal pack. It is not necessary to be precise to the tenth of a gram and for this reason dermatologists and dermatologists recommend getting used to using the equivalent capacity of a teaspoon of coffee (3 grams) for face and neck, the same for each arm and a soup spoon (6 grams) respectively for each leg, for the back, for the chest and for the abdomen.
Putting half the necessary cream doesn’t just halve the SPF number as many believe: the reduction is equal to the square root of the starting protection factor. An SPF 30 therefore becomes just over 5.
(Olaf Kraak/Getty Images)
When you put on sunscreen
The sunscreen should be applied before exposing yourself to the sun, so it is advisable to spread it before going outdoors, for example to go to the beach or generally for a walk. Repeating the application periodically not only serves to reduce the risk of leaving areas of the skin unprotected, but also to restore the layer of cream which tends to shrink and remove over time.
What gives protection is in fact the layer of sunscreen itself: it works as long as it is present. Especially in summer, perspiration is one of the main causes of its rapid reduction, as is any other mechanical action on the skin, such as putting on and taking off clothes. Some manufacturers still indicate on the packaging the ability of the cream to resist water, but proving it is not always easy and for this reason it is advisable to reapply the sunscreen after a bath. Even the action of the grains of sand can partially wear away the protection, however.
And the clothes?
There are many different fabrics and as a result some filter UV rays better than others. The denim in jeans, for example, has a good ability to block ultraviolet rays, while lighter fabrics like the cotton in T-shirts don’t do much. However, for some time now there have been swimwear, trekking clothes and other clothing made with technical fabrics with a high protection factor, usually indicated on the label. These products must be washed carefully and using specific detergents to reduce wear on the layer that protects from the sun’s rays.
Tan level
There is a rather widespread belief that using sunscreen “you tan less”. In reality, using sunscreens tans more slowly, because as we have seen, tanning is a defense mechanism of the skin: sunscreens are part of that protective work. In the end you get a tan anyway because, as we have seen, sunscreens are unable to fully protect.
However, the level of tan is commensurate with your phototype and in general with how you are made. Arrived at the maximum possible, there is no further tanning. Not using or using little sunscreen puts the skin under great stress and can be very risky to health.