Part 1: Understanding the sun

I am pretty sure that anyone who reads this article knows that the sun burns the skin. However, how is it concretely possible? How can this star so essential to our survival, at the same time be so harmful for us?

To understand everything, you must first know that the sun emits energy in the form of waves (solar energy). We can also classify them according to the length of their waves and, in fact, their particularities.

The first class is the famous UV rays (ultraviolet). We find UVA, UVB and UVC rays. UVA rays are about 96,5% of all ultraviolet rays that go to earth, while UVB is only 3,5%. Each, having different wavelengths (UVB: 280-320nm UVA: 320-400nm and 350nm UVC: 100-280nm).

The second class is the visible rays. As the name suggests, these are the ones we can see with the eyes. FInally, the third class is the infrared rays.

UVA and UVB are the ones that interest us the most to understand the effect of the sun on the skin. UVAs are hardly absorbed by the ozone layer, and indeed, 95% get to the surface of the Earth. UVB, in turn, is absorbed largely by the ozone layer (5% arrive at the ground).

* The UVC, they are extremely dangerous, but luckily for us, they do not arrive (at least at the time of writing these lines, on the surface of the Earth).

Specifically, what are their effects on our skin and why should we be wary?

Overall, UV rays act in many ways on the skin, some with immediate consequences and others with long-term problems.

One of the most obvious consequences is the induction of the inflammatory response of the skin leading to sunburn. Do you know when you go to bed at night after a day spent in the sun without sunscreen? You're hot, then cold, then you shiver ... well that's exactly what you're experiencing ... the inflammatory response!

Another effect of the rays on the skin is the activation of melatonin, leading to tanning. Basically this activation would help protect the skin from the damage caused by the sun ...


UVA, by their wavelength, can penetrate far into the skin. They are the main ones responsible for the aging of the skin (ie: wrinkles, pigment spots), tanning and sunburn. Until recently, scientists believed that the latter did not cause damage to the epidermis (place of several skin cancers). However, new studies have shown that UVA reaches the basal layer of the epidermis and could contribute to the development of skin cancer.

Be careful, the UVA rays can penetrate through the glass and windows, and they reach the surface of the Earth quite continuously throughout the day.


UVB, they are more strongly related to damage to DNA, and thus give the sun a carcinogenic effect quite marked! They are also partly responsible for tanning and aging of the skin. However, unlike UVA, they are lucky to be blocked by glass and have a peak intensity between about 10h and 16h.

The UV index

You have probably already noticed when you check the weather an indicator called UV index. In fact, it is a measure of the intensity of UV radiation emitted by the sun and the risk it represents for us. The scale goes from 1 to 11 +. The higher it is, the stronger the radiation, the more dangerous it is! The global health organization has decided to build it so that it can be standardized around the world.

It serves as a guide for us and tells us when to be even more vigilant about our exposure to the sun! While it is recommended to protect yourself at all times, it is a good indicator of when to further limit our exposure. Perhaps not the best idea of ​​the century to go swimming in the sun when the index is 8! ... you understand the principle!

In conclusion, UVA and UVB have their own peculiarities, but both can cause significant damage to the skin. It is therefore very important to protect yourself well, all year long, good weather, bad weather. Watch the 2 part of this series on the sun where you will learn more about sunscreens!

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