Why Do We Get Tanned in the Sun?

It is very likely that you have wondered why your complexion acquires a brown tone after exposure to the sun. We review the reasons behind it.
Why Do We Get Tanned in the Sun?
Diego Pereira

Reviewed and approved by el médico Diego Pereira.

Last update: 02 January, 2023

Natural or artificial tanning is widely accepted in today’s society. People sunbathe on their balconies, at the beach, by the pool, and on tanning beds to get that signature tan skin tone. However, most of them are unaware of the mechanisms behind this change. That’s why today we’re going to find out exactly why we get tanned in the sun.

Why we get tanned in the sun: initial considerations

As experts warn, human skin is repeatedly exposed to environmental factors that damage its DNA. Because of this, it has a series of endogenous mechanisms to protect itself, and reduce and repair such damage.

Since ultraviolet radiation (UVR) is one of the main environmental factors that directly affect the skin, it’s natural that protection strategies have been developed against it. The mechanism in the skin to mediate physical protection against the DNA-damaging effects of sunlight is estimated to have evolved in our ancestors a million years ago.

The process is very complex, and even today new methods are still being discovered by which the skin is protected from sunlight. Ultraviolet radiation is classified into three types: UVA, UVB and UVC. UVA describes the longer wavelengths (320 to 380 nanometers), UVB the mid-range wavelengths (280 and 320 nanometers), and UVC the shorter wavelengths (180 and 280 nanometers).

The danger of ultraviolet rays

Specialists point out that UVB and UVA rays are partially filtered in the atmosphere, but the percentage that reaches the Earth’s surface is significant. 100% of UVC rays are filtered before reaching the ground. The effects of UVB rays are mainly limited to the epidermis, while UVA rays due to their characteristics can affect the cellular and extracellular structures of the dermis.

Although a certain degree of exposure to these wave frequencies is healthy (they’re metabolized to create vitamin D, for example), an excess creates complications. Sunburn, petechiae, age spots, and skin cancer are the most common examples.

Why does the skin turn brown in the sun?

A woman tanning.
Melanocytes are skin cells that are activated by sun exposure, which create a natural tan.

Skin tone is related to the presence of a number of cells that, in principle, contribute to its defense against solar radiation. Although it isn’t the only one that fulfills this function, the most important pigment that mediates skin color is melanin. A group of cells called melanocytes produce the amount of melanin needed to maintain skin color.

This hue is an evolutionary trait that serves as protection from UV rays. It’s for this reason that those who live in areas with less solar radiation have lighter complexions than those who live in areas with greater solar interaction. That being said, exposure to ultraviolet radiation from the sun induces an increase in a process known as melanogenesis.

A biochemical mechanism is what causes the synthesis of melanin. A stimulation of its production causes a greater dispersion of UV rays. In the same way, it acts as an absorbent filter that reduces the penetration of rays through the epidermis. As a consequence, the skin turns brown with exposure to the sun as a defense mechanism to avoid the damage that radiation does to DNA.

The natural photoprotection factor (SPF) of this process is around 4. This means that between 50 and 70% of the sun’s ultraviolet rays are blocked. People with lighter complexions scatter and filter UV rays less than those with darker complexions. It’s for this reason that the different types of skin cancer are more common in white people

The importance of sun protection

The sun and brown skin are associated with the use of sunscreen.
Sunscreens are an easy-to-use, affordable, and affordable option to avoid complications from sun exposure.

So, you now know why skin turns brown on exposure to the sun. But we can’t finish this article without mentioning the importance of using sunscreen and other preventive resources to reduce the likelihood of complications. Far from being a whim, smearing the skin with a sunscreen agent, minimizing direct exposure, and wearing clothing to reduce exposed areas are all a must.

Do this especially if you live in a hot area, have a fair complexion, and have a history of skin cancer in your family. Remember that this type of cancer is the most serious complication, but others such as burns, spots on the skin’s surface, loss of elasticity, wrinkles, premature aging, and others are also very common. Be cautious, especially when using artificial tanning.

  • Brenner M, Hearing VJ. The protective role of melanin against UV damage in human skin. Photochem Photobiol. 2008 May-Jun;84(3):539-49.
  • Solano F. Photoprotection and Skin Pigmentation: Melanin-Related Molecules and Some Other New Agents Obtained from Natural Sources. Molecules. 2020 Mar 27;25(7):1537.
  • Thingnes J, Oyehaug L, Hovig E, Omholt SW. The mathematics of tanning. BMC Syst Biol. 2009 Jun 9;3:60.

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