Sun Protection SPF and UV Radiation Explained
Solar energy can be divided into 3 types of radiation:
1. infrared radiation (IR), responsible for heating of the skin
2. visible light
3. ultraviolet radiation (UV)
There are 3 groups of ultraviolet radiation.
- UVC rays are the shortest wavelengths and only reach the surface of the Earth in small amounts. They are generally stopped by the ozone layer.
- UVB rays, whose waves are of medium length, are responsible for slow tanning, sunburn, aging of the skin and skin cancer.
- UVA rays, with the longest wavelengths, are responsible for immediate pigmentation, as well as aging of the skin.
Do not confuse the UV index with SPF (sun protection factor).
The UV index is a universal scale ranging from 1 (weak) to 14 (extreme) that expresses the intensity of ultraviolet radiation and the risk that it represents for health when the sun is at its highest in the sky.
The main factors that influence the UV Index are geographical location (latitude and altitude), date, cloud cover and the thickness of the ozone layer.
The UV Index was developed by a Canadian team at the beginning of the 1990s. Nowadays it is the criterion recommended by the World Health Organization (WHO) in terms of informing the public of the risks linked to overexposure to the sun. A number of national bodies have adopted slightly different terms to categorize the UV level.
UV Index Risk level
7,8 Very high
9 and over Extreme
You can consult the UV index on the weather page of newspapers or on the Internet.
S.P.F. a sun protection Factor against U.V.B. rays
IP (Indice de Protection), FPS (Facteur de Protection Solaire), or SPF (Sun or Sunburn Protection Factor) are indices that determine the protection against UVB rays, evaluated using a method that has been validated at a European level and scientifically recognized by the FDA, the Food & Drug Administration in the United States.
The SPF index is calculated according to very strict standards:
- using tests carried out on volunteers (in vivo test)
- with a standardized light source that reproduces tropical sunshine
- with a suncare product applied to the skin in an amount of 2 mg/cm2
The principle is simple: a doctor marks out zones on the skin of the back; he applies suncare products of different factors to one half of these zones; he does not apply anything to the other half – the zones are free from any product.
The doctor then assesses the time that passes before the appearance of sunburn (erythema), with and without the use of the suncare product. The SPF index is the relationship between these two periods of time.
SPF = MED with sun protection / MED without sun protection, where MED = Minimal Erythemal Dose
An SPF is calculated for each subject tested. The overall SPF is the average of the values found for each of the subjects.
SPF thus corresponds to a multiplying factor. The higher the factor, the greater the protection. For example: with a factor of 10, the skin will take 10 times longer to burn than if no cream were applied. If, for a given person, the skin turns red after 5 minutes without protection, with a product with a factor of 20, it will take 5 X 20 = 100 minutes before turning red.
- Reapply sunscreen/sunblock regularly and after swimming.
- Avoid exposure when the sun is at its strongest, or cover up. Sunburn is dangerous, especially for children.
- Use sun protection products that are suitable for your skin type.
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