The UV Index is a measure of the intensity of UV radiation. The higher it is, the greater the potential for skin and eye damage, and the less time it takes for the harmful effect to appear. From what index do we tan? When to wear sunscreen? Answers with Dr. Paul Dupont, dermatologist.
[Mise à jour le 14 juin 2022 à 15h16] UV radiation is beneficial to our bodies in small amounts. It is in particular essential for vitamin D synthesis. But’prolonged and excessive exposure to sunlight can have harmful impacts on our health, especially on the eyes (inflammation of the cornea, eye cancer, cataract…), the skin (sunburn, premature aging of the skin, cancer of the skin, etc.) and on the immune system (reduction of immune defenses against infectious diseases, increased risk of the appearance of cancers). L’Universal UV Index sunscreen was developed by the WHO to to raise awareness the public and alert people to the need to adopt protective measures when exposed to UV.
What is the UV index?
The Universal Solar Radiation Index or UV Index was developed under the aegis of theWorld Health Organization (WHO). It reflects theintensity of UV (UltraViolet) radiation from the sun. The UV index is communicated for a slice of 2 to 4 hours around solar noon, i.e. around 2 p.m., legal French summer time. “This index finger is major in summer at the edge of the beach and in sunny anticyclonic weather between 11 a.m. and 4 p.m.; or thewinter in the mountains because it becomes more and more stronger when you go up in altitude” informs Dr. Paul Dupont, dermatologist in Toulouse, former hospital attaché in dermatology. In general, the UV index is also higher at the equator than in the temperate zone.
| The UV indices should not be confused with the sun protection indices appearing on the packaging and the explanatory leaflet of the sun protection products. |
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What is the UV index scale?
The values UV index start from zero and are increasing. The UV indices are divided into five classes:
- 0 to 2 inclusive (low risk),
- 3 to 5 (moderate risk),
- 6 to 7 (high risk),
- 8 to 10 (very high risk),
- 11+ (extreme risk)
The higher it is, the greater the potential for skin and eye damage., and the less time it takes for the harmful effect to appear. It is therefore necessary to protect yourself even more from radiation.
From what UV index should I wear sunscreen?
A sun protection is recommended from a UV index of 3. As the National Cancer Institute reminded us in an inventory published in 2021 “there is no such thing as a healthy tan : tanning constitutes an aggression of the skin”. Skin pigmentation (or tanning), whether induced by UVA or UVB, is accompanied by chemical alterations of DNA for doses lower than those triggering sunburn. Also, some people are more sensitive to UV rays than others. The tskin type, or “phototype”, is an important criterion. Particular vigilance is recommended for people with fair skin and red or blond hair, for whom tanning is difficult.
To prevent sunburn it is advisable not to expose yourself between 12 p.m. and 4 p.m., times when ultraviolet rays are most intense in mainland France. It is recommended to wear sunglasses, a t-shirt and a hat and to apply a Solar cream in sufficient layer on all parts by promoting high protection indices (minimum index 30) active against both UVB and UVA rays. This application of sunscreen must be renewed every 2 hours and after swimming. The index of sunscreen should be chosen according to your skin type. “The lighter the skin and the more intense the sun, the higher the UV index of the sunscreen should be.” informs Dr. Paul Dupont. Even when your skin is already tannedyou should protect yourself with sunscreen. The skin is less susceptible to sunburn but she is not not protected against the risk of cancer. “You should also know that to obtain optimal protection when the whole body is exposed to the sun between 11 a.m. and 4 p.m., approximately 50 g of product should be used, which is generally equivalent to a tube of cream: that is to say that it is generally difficult to protect yourself really and completely during periods of the day when the UV index is maximum” emphasizes the dermatologist.
What does the UV index presented to the weather report correspond to?
The values of the UV index vary throughout the day, like the intensity of solar radiation. When reporting the UV Index, the emphasis is on its maximum value on a given day. This is reached during the two hours preceding and following solar noon. Depending on the geographic location and whether or not summer time is applied, solar noon is between noon and two o’clock in the afternoon. The media usually presents a forecast of the maximum UV index for the following day.
What time is it at the most?
The UV index is at its maximum at noon solar time (2 p.m. in France in summer), when the sun is highest in the sky. The higher the sun is in the sky (short shadows), the shorter the path of the rays in the atmosphere, the stronger the UV index. Whereas when the sun is low in the sky (long shadows) the more UV rays pass through a thick layer of atmosphere and the lower the UV index.
What do the UV indices 1 and 2 mean?
A UV index of 1 or 2 is said weak. “This only leads little risk of reaction except for people with a clear phototype and who lack certain vitamins (especially B vitamins). They may feel tingling or even irritation on the uncovered parts“says Dr. Paul Dupont. Sunglasses should be worn. For children and adults with sensitive skin, the sunscreen must have a sun protection factor of 8 or 10.
What do the UV indices 3, 4 and 5 mean?
A UV index of 3 to 5 is moderate. Without protection, it is necessary to wear sunglasses and a hatto get in the shade between 11 a.m. and 4 p.m., the hottest hours of the day. When the UV index is 3 to 5, you must also apply sunscreen. For children and adults with sensitive skin, a protection factor of 15 is necessary. For adults with dark skin, a protection factor of 8 is sufficient. “However people sensitive to the sun should use a screen between 30 and 50“says Dr. Paul Dupont.
What do the UV indices 6 and 7 mean?
A UV index of 6 or 7 is a UV index raised. You must use sunglasses, cover up (shirt or T-shirt) and wear a hat between 11 a.m. and 4 p.m. and apply sunscreen. For children and adults with sensitive skin, a protection factor of 50 is recommended.
What do the UV indices 8, 9 and 10 mean?
A UV index of 8 to 10 is a UV index very high. It is recommended to wear sunglasses, cover up, put on a hat and davoid any exposure by going in the shade between 11 a.m. and 4 p.m. or ideally by not going out. Sun protection should be reinforced. The children should be protected with sunscreen protection factor 50.
What is the maximum UV index?
A UV index of 11+ is extreme. These are the maximum indices. the risk of burns is very high. It is recommended for adults with sensitive skin and of course for children not to expose themselves to the sun. Adults with dark skin should protect themselves with sunscreen with a protection factor of 40. The maximum UV index is 11 or more. Outdoors should be avoided if possible.
Thanks to Dr. Paul Dupont, dermatologist in Toulouse, former hospital attaché in dermatology. Author of: “Natural care for your skin”, Editions Eyrolles, 2016 and “The physical, psychic and spiritual foundations of health”, Traditional Diffusion Editions, 2020.
Sources:
The universal index of solar UV radiation. WHO. 2002
Ultraviolet radiation and cancer risks. Reference sheets. National Cancer Institute. October 2021.