Sun creams - sun protection
Solar radiation, source of life but also source of danger
The sun emits a set of light radiation that reaches the surface of the earth: the ultraviolet (uv) visible and infrared (ir). uv, as a whole, does not exceed 5% of total energy, but their impact on organic molecules is very important and this leads to considerable physiological responses in all areas of life. uva, uvb and uvc are characterized by different wavelength beaches. the energy of each radiation depends on its light source (e.g. the sun) and the environment in which it spreads (the Earth's atmosphere if the source is the sun).
What differences between uva, uvb and uvc ?
- Solar radiation uva:
The uva cross the glass. their wavelengths are between 320 and 400 nm. the short uva (or wat 2) between 320 and 340 nm and the long wava (or uva 1) between 340 and 400 nm. 98% of those who reach the earth are uva.
Less energy than the uvbs, they have greater penetration power in the skin and 20% to 30% reach the average dermis.
Uva stimulate the synthesis of melanin: it is the "tuva tan" or delayed pigmentation.
The uva have no direct toxicity, but their radiation generates the production of free radicals, extremely reactive molecules of short life. these free radicals amortize reactions in a chain of 1'adn, proteins and lipids and therefore generate cancer cells. the incidence of uva in certain epidermal tumours (epleptoid carcinoma) has been clearly established. uva are also considered as a factor promoting the risk of melanoma. molecular alterations induced by uva are also at the origin of premature aging of the skin and especially the structures of dermis. the soluble collagen/collagen ratio decreases to the point of varying the mechanical properties of the skin (elasticity, thickness). When these skin changes are accompanied by a thinning of the epidermis, the appearance of wrinkles and pigment spots, all of these changes are grouped under the name of solar elastosis.
- Solar uvb radiation:
Uvbs are responsible for solar erythema (sun cut) which has its maximum intensity 24 hours after exposure. this reaction stimulates the process of melanogenesis of the skin at the origin of delayed pigmentation, process also attributed largely to uva.
Their strong energy can cause necrosis of epidermis cells. These damaged cells are called sunburn cells and release chemical mediators who contribute to inflammatory sunburn demonstrations. the important energy of the uvb also allows them to generate molecular disorders (alteration of certain bonds of the adn and proteins) that in the long term, and if they renew, saturate the system of repair of the adn. This leads to "mistakes" in the genome of the affected cells, causing skin cancers. That's why we're talking about direct toxicity to uvbs.
- Solar radiation:
The uvc correspond to the fraction of the uv which is transmitted only in the air. These are the radiations whose wavelengths are the shortest (190 to 290 nm), so they are extremely energetic.
This energy gives them considerable alteration power on biological molecules. they are used for their germicide activity in hospitals. one of their targets being the aden, they have a very important carcinogenic potential.
If all the uvc generated by the sun reached the surface of the earth, the toxicity they would generate would be such that life would be impossible.
Solar radiation is not constant
The quality of radiation on the surface of the earth is not constant. the intensity of the uv is all the more important if:
- the equator is approached and the altitude is increasing: at 1500 m, there are 20% more water than at sea level.
- between 12 and 16 legal hours (10 and 14 solar hours): 50% of the daily inuv energy is delivered during this period.
- soil reflection increases: it is 10% for sea water, 15% to 25% for sand and 50% to 85% for snow.
Adapted solar protection from childhood
The carcinogenic power of the uv is clearly established for cancers of the epidermal part of the skin: these are epidermal and spinocellular carcinomas. As for cancers that reach the dermis, it is shown that some malignant melanoma occur ten to twenty years after a sunburn during childhood.
The sun sensitivity (phototype) of children and adolescents must be assessed. a clear skin subject, for example, will never have protective tan. under the action of the uv, its skin preferentially produces a red pigment that not only does not protect, but releases free radicals, toxic to the skin. the declaration of these attacks is often the result of overexposures in the early years of life.
This is why a suitable photoprotection, introduced from childhood, significantly limits the risk of skin cancer. Source:https://www.pediatre-online.fr/
Sun protection and skin cancer
A reminder of the basic recommendations: cover, seek shade, do not brave the sun at noon and always, always, use sun protection.
Otherwise, we are told, we must face the consequences of premature aging of our skin: early wrinkles and the risk of developing skin cancer.
Unlike what says, application every 2-3 hours, research has shown that the best protection is ensured by application 15-30 minutes before exposure, followed by a new application 15-30 minutes after sun exposure. the application must be renewed every 2 hours. a new application is also necessary after activities such as swimming.
It does not kill as often as other cancers, such as lung and breast cancer, but it killed 1570 people in france in 2010, according to the National Cancer Institute.
Skin cancer cases have tripled over the last 20 years, while very few of us used sun creams. It is believed that the framework of the public health mission is to convince the largest number of people to protect themselves with sunscreen. but curious thing: both the rate of skin cancer and the use of sun cream increased simultaneously.
Sun creams can cause more trouble than advantages
Today, most solar creams are "wide spectrum," that is, they protect against ultraviolet rays a (uva) and ultraviolet b (uvb).
Uva and uvb pass through the clouds and are responsible for premature skin aging. this premature aging has been associated with sunburn for some years.
The uvb is known as "slayer ray" because it causes solar erythemes.
We might believe that we don't use the products properly, and we spend more time outdoors.
One might also think, since skin cancer takes years to manifest itself, it is too early to draw conclusions.
Increasing use of sun protection and that of skin cancers can be considered a paradox. but some scientists have long feared that chemicals commonly used in sun creams can cause more trouble than advantages.
Can sun creams cause damage to the aden ?
The solar protections we currently use are chemical or physical solar filters.
The dr stephen antczak, co-author of cosmetics unmasked, explains the difference: "physical solar filters contain materials that reflect ultraviolet rays. Chemical solar filters contain molecules that absorb ultraviolet rays and reduce their energy.".
These chemicals that can alter ultraviolet rays are both complex and powerful.
The three most commonly used molecules in solar creams are: para-aminobenzoic acid, cinnamates and benzophenols.
A sun cream that absorbs energy cannot destroy it however. The dr john knowland, biochemist at the University of Oxford, is concerned with absorbing screens: "the uv react with light and therefore interfere with the skin, causing damage to the adn - one of the possible causes of cancer.".
Do solar creams cross our skin ?
There are reports that claim that chemicals used in sun protection, a little like nicotine for patches, can penetrate the skin.
Kim erickson, author of "you protect against the hidden dangers of cosmetics," quotes a study of the queensland laboratory in australia, where oxybenzone, chemical sunscreen, crossed the protective barrier of the skin.
The scientists of the sahlgrenska university in suede showed that benzophenone-3 (B-3), another chemical absorber inuv, is appeared in the urine volunteers having applied the recommended amount of sun cream, in some cases up to 48 hours later.
In Switzerland, researchers conducted five tests with chemicals commonly used in solar creams. they found that these products all acted as estrogen. one of the tested chemicals was found in breast milk.
The environmental network of women suggests that "These substances are not only absorbed by our skin but they accumulate in our fatty tissues.".
The above researchers call to the caution and more research.
Does the sun cream work like a defense ?
Although manufacturers do not say that, there is a false popular idea that sun creams would protect from skin cancer.
Solar creams were tested on laboratory rats to protect against spinocellular cancer. this cancer is one of three types of skin cancer. it occurs more frequently than melanomas (potentially fatal), but much less than baso-cell cancer, the most common. evidence was not sufficient to conclude the use of solar cream in the protection against spinocellular cancer.
According to a research group of oms, including scientists, doctors and manufacturers of solar cream, "no conclusion can be drawn as to the use of solar cream against basocellular carcinoma and skin melanoma".
Exposure to uv rays, even with sun cream, is likely to be a risk factor.
Dermatologists inform that a sunburn increases the sensitivity to skin cancer.
Sun protection products do not do everything, the genes also have importance
"The biggest problem with skin cancer is your genes," says the gasparro dermatology professor "Some people can be able to stay in the sun longer than others - but you can't give this as a public health message. "
The idea is to transmit simple information, taking into account all the messages and to follow the recommendations of the dermatologists on the use of solar creams.
However, in recent years, dermatologists and cancer research groups have demoted solar protection as a defence in third place - for occasions where you can absolutely not cover yourself or avoid going out to the sun.
Melanin and sun protection
♪ melanin are among the main biological pigments responsible for skin coloring in the human being.
These are the melanins that make us tan, thus protecting the adn from skin cells from ultraviolet rays (especially uvb) of the sun.
During a prolonged sun exposure, bronze is made as the body produces more melanin, so we are better protected against uv.
Melanins act by absorbing the uv and restoring the energy received in the form of heat.
Eumelanin (black pigment) is much more effective in this role than pheomelanin (clear pigment) that protects very little, and decomposes easily under the effect of uv, liberating free carcinogenic radicals. This is why redheads are more fragile than browns. blonde people are also very fragile in the face of the sun.
Even for matt or dark skins, the protection offered by melanin is far from total. Too large adensities can lead to cancer of skin cells.
Sun protection factor (fps)
Enanz greiter defined the concept of sun protection factor (fps) in 1962. It has become a global standard to measure the efficiency of a sunscreen when applied at a minimum rate of 2 milligrams per square centimetre. you will also find it on the bottles under the name spf for "sun protector factor"
Fps is a laboratory measure. the more important the fps is, the more important the UV-B protection (ultraviolet radiation causing sunburn) is.
So, with a sunscreen fps 50, your skin will not burn until it has been exposed to 50 times the amount of solar energy that should normally burn it.
The amount of solar energy you are exposed to does not depend only on sun exposure, but also on the moment in the day. Sun rays are weaker in the morning and evening than at noon.
In practice, the protection of a sunscreen depends on several factors:
- the type of skin of the user,
- applied quantity and application frequency,
- its activity ( swimming for example results in a loss of sun cream on the skin,),
- the amount of sun cream absorbed by the skin.
The pf is an incomplete measure because the invisible damage and aging of the skin are also caused by ultraviolet a (uva, wavelength from 320 to 400 nm), which cause neither redness nor pain.
Based on a study conducted in 2004, the uva also causes damage of the adn cells deep in the skin, which increases the risk of malignant melanoma.
Even some sun creams "wide spectrum uva / uvb" do not provide sufficient protection against uva rays.
Sun protection against water
The best protection against uva is ensured by products containing: zinc oxide, avobenzone, ecamsule or titanium dioxide. the latter probably gives good protection, but does not fully cover the entire spectrum,UV-A. According to recent research, zinc oxide would produce more protection than titanium dioxide in wavelengths between 340 and 380 nm.
According to Professor knowland of the University of Oxford, "if such particles can more easily penetrate human cells, the file has not yet been treated sufficiently.".
Concerning titanium oxide, the Scientific Advisory Committee of the European Commission on Cosmetics, informs that the compound is "conformed to regulation and safe for use in cosmetic products".
The different phototypes
PHOTOTYPE 1 : you have a very clear skin, white hair (albinos) or roux, rustic spots that appear very quickly in case of exposure.
- never seek to sunbath, protect yourself in all circumstances of the sun (cloths, hats, glasses...)
- protective cream : total screen
PHOTOTYPE 2 : you have a very clear skin, which can become hauled, light blonde or chestnut hair, stains of roussors that appear in the sun.
- don't want to tan. you must use maximum protection and expose yourself to the sun
- protective cream: screen of a index greater than 30
PHOTOTYPE 3 : you have a clear, but easily bronze skin, blonde or chest hair, little or no rustle spots.
- you can expose yourself to the sun, but progressively and limitedly
- protective cream: screen of a index greater than 15
PHOTOTYPE 4 : you have a matt skin, which bronzes very easily, chest or brown hair, no routing spot.
- you can gradually expose yourself
- protective cream: screen of a index greater than 10 in the first days
Phototype 5 or 6 : you have naturally pigmented skin or black skin.
- you can gradually expose yourself
- moisturizing cream
Is the fps still suitable for solar creams ?
The minimum application according to the definition of fps is 2 milligrams per square centimetre of skin to be protected. A quick calculation allows you to find that for an average adult, you should use at least 30g of sun cream by application.
Unfortunately, "this information is useless, because people rarely use it" according to Professor Brian diffey, Director of Clinical Services at Newcastle General Hospital.
It suggests that manufacturers reduce the amount of solar product used in the test to reflect what people actually use.
But if the repository is to evolve, it should be done at the same time in all countries. without this armouring of the norm, the comsumers would no longer find themselves there.
Sun cream and vitamin d deficiency
Uv rays are responsible for the synthesis of vitamin d. use of sun cream reduces the synthetic capacity of vitamin d by the skin. This can lead to vitamin d deficiency in order to avoid this, here are the recommendations of Professor holick, one of the world's leading vitamin d specialists:
"I recommend that people exhibit for a duration that varies depending on the time of year, time of day, latitude and degree of skin pigmentation. If you know that after 30 minutes of exposure you get a slight sunburn, I recommend an exhibition between 10 and 15 minutes of arms and legs, or abdomen and back if you are in bathing suit, and this 2 to 3 times a week. You have to wear sun protection on the face that is the most sensitive area. Go out, expose yourself to the sun, then, if you plan to expose yourself longer, put a sunscreen. "
Real / false on sun and skin cancer
Sunburns are the first stage of tanning: fake
In any case a sunburn is already a skin lesion. "light" sunburns cause, in addition to pain, a thickening of the skin. if the sunburn is more important (burning, cloaks,) the skin "painting" and leaves room for a new, more fragile fabric, which can burn in turn. It's a vicious circle !
Better bronze with a product with low protection index: real
If we have a skin suitable for tanning. but you risk catching sunburn more easily. because if, for subjects with matte skin, sunburns do not occur as quickly, they still exist. and the skin suffers damage.
Everyone can sunbathe, just put the dose there: fake
Some individuals, such as redheads, produce little or no brown pigments that allow tan.
The sun promotes the treatment of certain diseases: true and false
- rachitism (but 10 minutes of exposure per day are enough)
- psoriasis (in combination with other treatments)
- the eczema
- joint pain (it is better to treat the cause), even if the heat does good
You have to watch all the beauty grains: real
The term "grain of beauty" refers to several types of skin pigmented lesions: warts, papillomas, naevus. only lesions containing cells made of melanic pigment, known as naevus melanocytaires, can cause skin cancers. but in doubt, a "grain of beauty" that changes appearance, bleeds, stretches or whose color changes must lead to consulting his doctor.
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source: https://www.lanutrition.fr / www.ligue-cancer.net