Why do we get sunburn?

The sun emits heat, light, as well as UV rays. Among these UV rays, we distinguish three different types:

• UVC Rays : These are UV rays that are the most harmful, but they are completely filtered by the ozone layer. Therefore, they do not reach our skin.

• UVB Rays : Due to their short wavelength, UVB rays have a low penetration into the dermis. They are responsible for tanning as well as sunburn. They also promote premature skin ageing, as well as skin cancers.

• UVA Rays : These are the rays that penetrate the deepest into the skin at the dermis level. They cause the formation of free radicals (oxidative stress) which reduce the skin's natural repair capacity. Furthermore, an abnormal accumulation of elastin fibres and collagen fibres is observed in the dermis. This is explained by the effect of UVA rays on DNA. The observed results are skin sagging, and the early appearance of wrinkles and spots. Moreover, being genotoxic, UVA rays induce alterations at the DNA level with the emergence of cancerous cells.

UVB rays, which penetrate the dermis to a lesser extent, are responsible for tanning as well as sunburn, also known as actinic erythema. At the skin level, a sunburn manifests as redness, pain with itching (pruritus) and the appearance of blisters (phlyctene). These symptoms are the result of ainflammatory process leading to a dilation of the blood vessels and a reddening of the skin. This reaction appears8 to 24 hours after exposure.The healing time of a sunburn varies depending on the degree of the burn.

The inflammatory process behind sunburn is still not fully understood, but a study has shown that when the skin is exposed to UVB rays, keratinocytes release intracellular RNA which stimulates the production of pro-inflammatory molecules (cytokines and interleukins) that cause the symptoms of sunburn.

It is important to note that sunburn can occur without direct exposure to the sun. Indeed, UVB rays are present regardless of the weather and they are reflected by water, sand, and snow.

Sunburn increases the risk of premature skin ageing with the emergence of wrinkles and spots, as well as the development of skin cancers, particularly melanomas, due to UVA and UVB rays which are genotoxic.

We distinguish three types of sunburn :

• Sunburn with first-degree burn :

  This type of sunburn is characterised by the presence of bright red and painful lesions on the surface of the epidermis and theabsence of blisters. Subsequently, a more or less significant peeling is observed. The healing duration is 2 to 7 days without leaving any spots or scars provided that the skin is well cared for.

• Superficial second-degree sunburn :

  The symptoms are identical to those of a first-degree burn, including the presence of blisters filled with a clear fluid (phlyctenae) at the level of the epidermis. General manifestations such as headaches, fever, and discomfort can also be observed. These symptoms may indicate heatstroke or dehydration.In this case, the healing process will be longer and will take 1 to 2 weeks with a risk of spots and scars that may be slow to fade.

• Deep second-degree sunburn :

  This is the most severe case. The blisters have a pale appearance due to the destruction of blood vessels. Unlike the other two types of sunburn, here the pain is minimal as the nerve fibres have been burnt. The healing will take 1 month with a risk of persistent scarring.

Please note : Do not hesitate to consult your dermatologist for optimal care.

The risk of sunburn varies according to different factors:

• Age : Children burn 4 times faster than an adult because their skin is thinner. Therefore, infants under 12 months should not be exposed to UV rays.

• Light phototypes : Indeed, the lighter your phototype, the higher the risk of sunburn. Phototypes I to III are the most vulnerable.

• The use of photosensitising molecules : Whether in medications (such as isotretinoin) or in cosmetics (like AHAs and BHAs), the sensitivity of your skin to UV rays will be increased with a heightened risk of sunburn.

• Lack of sun protection : Sun protection is paramount as it provides you with protection against the harmful effects of the sun. Our face sunscreen provides broad-spectrum UVA/UVB protection and prevents photoaging.

• GALLO R. & al. Ultraviolet Radiation Damages Self Noncoding RNA And Is Detected By TLR3. Nature Medicine (2012).

• BERTHELEMY S. Conseil à un patient se plaignant d'un coup de soleil. Actualités Pharmaceutiques (2013).

• YUENG H. & al. Sunburn frequency and risk and protective factors : a cross-sectional survey. Dermatology Online Journal (2021).