Why does our skin get darker after being exposed to the sun? The secret behind UV rays

Why does our skin get darker after being exposed to the sun? The secret behind UV rays

We all know this: after spending time in the sun, our skin turns red or brown. Because? It is not due to the heat of the sun, nor to the light, but to the invisible ultraviolet radiation that reaches the earth from the sun. Basically there are UV-A, UV-B and UV-C rays. While the dangerous UV-C radiation is already intercepted in the atmosphere, UV-B and UV-A- reach us, the main part, ie 95%, of UV radiation consists of UV-A radiation. Long-wave UV-A rays have a wavelength of 315 to 400 nanometers, short-wave UV-B rays have a wavelength of 280 to 315 nanometers.

Radiant knowledge

In general, the shorter the wavelength of the radiation, the more dangerous it is. Visible light has a wavelength of 780 to 380 nanometers. In the microwave, food is heated with radiation whose wavelength is much longer than that of ultraviolet radiation: between 1 mm and 1 m. High-energy, short-wavelength X-rays, on the other hand, are much shorter, ie between 10 pm and 1 nanometer.

Visible reactions to invisible rays

The basic rule is: UV radiation penetrates our skin and this always leads to direct reactions that are immediately visible and always to indirect reactions that are only visible over a long period of time. Because they penetrate the skin to different depths, UV-A and UV-B rays have different effects on the skin.

UV-B rays

Only a small part of UV radiation, specifically 5%, reaches us as UV-B radiation. The rays reach the epidermis, that is, the upper layer of the skin, where they produce an immediate and visible reaction, namely redness, sunburn and tanning, depending on the duration of sunbathing. This is why it is often also referred to as UV burn radiation.

But that's not all: excessive exposure to UVB radiation can lead to the development of skin cancer in the long term. A distinction is made here between light skin cancer and highly dangerous black skin cancer.

Fact Box about skin cancer

Skin cancer is the most common form of cancer worldwide: the sun is the trigger. The World Health Organization (WHO) registers, according to conservative estimates, about 180,000 malignant melanomas (“black skin cancer”) worldwide every year [and between two and three million non-melanoma skin cancers (“clear”). In Germany, the frequency (incidence) of malignant melanoma has tripled in the last 25 years.

The light callus – When the skin wants to protect itself

One of the first reactions of the skin to harmful UV radiation are the so-called photocalluses. The top layer of skin thickens after prolonged exposure to UVB radiation, improving your own protection by four times. This roughly corresponds to a SPF 4 sunscreen. However, it takes two to three weeks for the callus to fully develop.

UV-A(ge) rays

Most UV rays, UV-A rays, penetrate the dermis. In the subcutaneous tissue, these UV-A rays trigger long-term structural changes that are the main cause of premature skin ageing. These consequences are not seen in the first years, but once these processes are started, they are irreversible.

UV-A: The number one cause of wrinkles

UV-A rays damage the skin's collagen and elastin, the same fibers responsible for a youthful appearance. Glycation is the reaction of collagen fibers with UV-A light: the network of collagen fibers is destroyed, individual collagen fibers can be damaged. Do nothing to counter the increase in wrinkles: the skin ages visibly, and usually even worse: the dreaded leathery skin with wrinkles develops.

UV-A: Leaves the skin flaccid

The loss of elastin, in turn, is responsible for sagging skin. To make matters worse, unprotected sun exposure also lowers the skin's hyaluronic acid levels, resulting in thinner, more vulnerable skin.

UV-A: Causes uneven complexion

To protect the skin, melanocytes in the skin react to UV radiation with excessive melanin production. Dark spots or diffuse patchy hyperpigmentation develop. This hyperpigmentation often occurs at a young age, for example during pregnancy or as a reaction to certain medications or hormones. In many people, excess melanin is produced unevenly and concentrated in smaller areas, resulting in stubborn pigment spots.

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