Tanning 101 — why we tan and the connection to skin cancer

Tanning is the body’s natural response to UV exposure. So why then, if it’s natural, is it so dangerous? The answer lies in why our skin tans in the first place. 

Why we tan

UV rays from the sun (and artificial sources) are the source of all tans. The sun emits three different types of UV rays: UVC, UVA, and UVB. UVC rays are the most powerful but rarely get through the earth’s atmosphere, which means they have very limited roles in tanning and skin cancer incidence, and it’s also why you may have never heard of them before.

UVB and UVA rays are the ones we need to worry about. UVB rays penetrate the top layers of the epidermis (the top layer of our skin), causing burning and delayed tanning. But UVA rays are the main culprits when it comes to tanning as they penetrate to the deeper layers of the epidermis and trigger our melanocyte cells to produce melanin. (As a side note: UVA rays are also largely responsible for aging as they break down collagen in the skin.)

What is melanin?

Melanin is the pigment in our skin, the substance that gives it color. It is our body’s natural defense against UV radiation as it reduces UV penetration into cells by absorbing the rays and transforming them into heat. This is why, although dark skin will still be damaged by UV exposure, lighter skin, which has less melanin in it, is more vulnerable.

How the tanning process works

When UV rays hit the skin, they darken existing melanin and cause a process called melanogenesis to occur. This is when melanocyte cells located in the lower layers of the epidermis generate new melanin, darkening the skin and forming a natural barrier against UV radiation. The tan that results from melanogenesis is a delayed tan, occurring after any existing melanin has been darkened. The problem with this new barrier of melanin is that it can only absorb limited amounts of radiation.


The FDA estimates that the protection created from the extra melanin in tanned skin only amounts to around an SPF of 2 to 4, meaning that it is severely limited (only blocking 50-75% of UVB rays at best). Once the skin has absorbed all of the UV radiation it can through its natural defenses, damage to the skin’s DNA occurs, which leads to sunburn and eventually can cause skin cancer.

From tanning to burning

When the DNA in our skin is damaged, the body responds by increasing blood flow to the dermis (the second layer of skin underneath the epidermis) to increase cell turnover in order to repair the damage. The result is what we know as sunburn. The pain of a sunburn is caused by an increase in inflammatory immune cells sent to the area and is designed to alert us to the damage, hopefully discouraging us from further sun exposure to the area. When the damaged skin cells die, they are sloughed off and the burned skin peels.

But what if you just want to get a ‘base tan’?

With the basics of tanning understood, the concept of a ‘base tan’ starts to unravel. While at first glance it may sound like a good idea to ‘prepare’ your skin before a beach holiday or a long day out in the sun, the fact is that any tan is essentially our skin trying to cope with the sun’s radiation by trying to prevent damage from occurring. And, as discussed above, the amount of protecting our skin’s natural defenses can provide is severely limited. The bottom line is that once the skin starts to tan, it’s usually a good sign that damage has already occurred.

The best way to protect yourself for a beach holiday or a period of high sun exposure is to apply broad-spectrum sunscreen regularly, wear sun-protective clothing and seek shade whenever possible.

And what about vitamin D?

The other main point of contention when it comes to tanning is the question of vitamin D, sometimes known as the sunshine vitamin. There is no doubt that vitamin D is essential for our health as it plays a role in proper immune function, the absorption of calcium and phosphorus and more. While the sun is typically the best source of vitamin D, it’s important to remember that a little sun exposure goes a long way. Most research points to as little as five to ten minutes of sun exposure two to three times a week on the arms, legs, hands and/or face to meet all of the body’s vitamin D needs.

Further, prolonged sun exposure will not increase the body’s stores of vitamin D. Rather, levels will remain steady, but the risk of developing skin cancer will greatly increase. The sun is also not the only way to get vitamin D. People can supplement with tablets or acquire it from certain foods such as fatty fish, some cereals and eggs; however, it is worth noting that the body will not readily store vitamin D without fat – so taking vitamin D supplements with something fatty such as olive oil can help in absorption.


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