Sun and your child's skin - what the experts say
Different types of radiation
Among the various types of solar radiation that reach of the Earth, there are three types that affect our bodies:
- visible rays (that the human eye can see),
- infrared (IR),
- ultraviolet (UV): UVA and UVB.
The ozone layer prevents UV rays with wavelengths of under 290 nm (UVCs) and the shortest UVB rays (280-290 nm) from reaching the Earth.
Effects on the skin
The effects on our skin vary depending on the rays’ wavelength: the greater a ray’s wavelength, the deeper it penetrates into our skin. So UVA and UVB rays have different consequences:
- UVB rays are responsible for tanning, sunburn, ageing of the skin and also skin cancer. They are harmful to our skin.
- UVA rays, which penetrate more deeply, are responsible for tanning but also for skin ageing and wrinkles. UVA rays are less powerful than UVB rays, but there are far more of them: they account for 98% of all UV rays, whereas UVB rays account for only 2%. Also, they remain constant throughout the day and throughout the year, whereas UVB rays are more powerful at midday and in the summer, and less powerful in the mornings, evenings and in wintertime.
- Good sun protection should be effective against both UVA and UVB rays.
The amount of solar radiation that our skin absorbs varies depending on many factors:
- Season: in July in the northern hemisphere, the risk of sunburn due to UVB rays is 100 times greater than in the wintertime.
- Latitude: the sun is at its strongest at the equator, where it is directly above us. It therefore has a shorter journey to make through the ozone layer.
- Altitude: the amount of UVB radiation increases by 4% with every 300 meter (or 1000 feet) increase in altitude. This partly explains why the risk of sunburn is so high in mountainous regions.
- Time of day: in the morning and the evening, the sun's rays are oblique. They cross the ozone layer more between 11 AM and 2 PM when UVB sunlight is at its maximum.
- Clouds: depending on the thickness and their altitude, they can filter the UV rays a little, but it is still possible to get sunburnt when the sky is overcast.
- The nature of the ground: reflective powers vary depending on whether there is snow on the ground (85%), sand (17%), water (5%) or grass (3%). So the mountains are particularly dangerous, with more UVB rays because of the altitude and greater reflective powers because of the snow.
- Water: it can reflect up to 20% of all UV rays, hence a risk of sunburn even underwater.