The sun emits radiation that penetrates the skin. Essential for our good health, these rays can also have harmful effects on the body. And when it comes to UV rays, a child's skin is more fragile than an adult's. The skin is less able to defend itself against the sun's harmful rays and retains the "memory" of sunburn for many years. Childhood is therefore a crucial period when it comes to sun exposure, and parents have a major role to play in protecting their child's skin. Learn with us about the dangers of the sun and how to effectively protect your baby!

Solar radiation

The different types of radiation

Among the solar radiation that reaches Earth, three types of radiation can be distinguished that have effects on the body:

• visible radiation (what the human eye perceives),
• infrared (IR),
• Ultraviolet (UV): UVA and UVB.

The ozone layer stops UV rays with a wavelength of less than 290 nanometers (UVC) and the shortest UVB rays (280-290 nm).

The effects on the skin

The effects of radiation on the skin vary depending on its wavelength: the longer the wavelength of radiation, the deeper it penetrates the skin. Thus, UVA and UVB have different consequences:

• UVB rays are responsible for tanning, sunburn, skin aging, and skin cancer. They are harmful to the skin.
• UVA rays, which penetrate deeper into the skin, are responsible for tanning but also for skin aging and wrinkles. UVA rays are less energetic than UVB rays, but they are much more abundant: they represent 98% of UV radiation, compared to only 2% for UVB rays. Furthermore, they are constant throughout the day and year, whereas UVB rays are strongest at midday and in summer, but weaker in the morning, evening, and winter. Therefore, good sun protection must be effective against both UVA and UVB rays.

The radiation received

The amount of solar radiation received by the skin varies depending on many factors:

• The season: in July in the northern hemisphere, the risk of sunburn due to UVB is 100 times greater than in winter.
• Latitude: the intensity of the sun is greatest at the equator where the radiation is vertical and therefore has a shorter path through the ozone layer.
• Altitude: the amount of UVB increases by 4% for every 300 meters of elevation gain. This partly explains the significant risk of sunburn in the mountains.
• The timing: in the morning and evening, the radiation is oblique. It passes more through the ozone layer between 11 a.m. and 2 p.m.: UVB radiation is then at its maximum.
• Clouds: depending on their thickness and altitude, they can filter some UV rays, but sunburn is still possible under a hazy sky.
• The nature of the ground: the reflectivity varies depending on whether it is snow (85%), sand (17%), water (5%), or grass (3%). Thus, the mountains combine all the dangers, with higher UVB radiation due to the altitude, and greater reflection from the snow.
• Water: it reflects up to 20% of UV rays, hence a risk of sunburn even underwater.

The effects of the sun on the skin

The positive effects

Sunlight triggers positive biological reactions, the main one being the synthesis of vitamin D. This vitamin stimulates calcium metabolism and promotes bone growth. The sun also has a beneficial effect on mood and can, for example, be used to prevent seasonal affective disorder (SAD).

The negative effects

However, solar radiation also has harmful biological effects, both in the short and long term:

- In the first few hours following exposure, two types of phenomena may appear, depending on the duration and intensity of the exposure and the phototype of the subject:

• The heat from infrared radiation can cause sunstroke, with discomfort and/or headaches, or even heatstroke, with acute dehydration and altered consciousness. This occurs mainly in children.
• The epidermis can be burned by UVB rays, and partially by UVA rays, resulting in sunburn.

- After several years, repeated exposure without appropriate and effective protection can lead to deterioration of skin cells:

• UVA rays accelerate skin aging and cause the destruction of the skin's elastic fibers.
• UVB rays, with the help of UVA rays, induce skin cancers through the mechanism of photocarcinogenesis. A distinction is made between epitheliomas, which appear as small, rounded, whitish or pinkish bumps or persistent scabs, and malignant melanomas, which appear on healthy skin or result from the transformation of a mole. To detect these melanomas early, it is important to pay attention to any mole that changes in appearance, whether in shape, color, or thickness, and not to hesitate to consult a doctor regularly.

Skin types have varying degrees of sensitivity to the sun

When exposed to the sun, the skin triggers natural biological defense reactions. The stratum corneum thickens, and cells called melanocytes produce a natural pigment, melanin, which gradually colors the skin: this is tanning. But not all skin reacts to the sun equally: depending on its ability to produce melanin and therefore tan, it is more or less resistant to UV rays. We can thus identify six levels of resistance. phototypes different: