Ultraviolet radiation (UV) is a type of energy emitted by the sun. It is known as Ultraviolet because it has a shorter wavelength than visible violet light and so is beyond the violet end of the visible spectrum.

Ultraviolet radiation is divided into three different bands based on the amount of energy each band contains : UVA, UVB, UVC. Each of these types of UV has its own characteristics and dangers.

Types of Ultraviolet Radiation


The earth’s atmosphere blocks the majority of the sun’s UV radiation, but enough of it still reaches us to pose a threat. By far the greatest portion of the UV radiation that does make it to earth is made up of UVA. UVA has the longest wavelength and the least energy. This not only allows it to penetrate the atmosphere more easily, but also to pass thorough cloud cover and normal window glass.

When UVA hits us, it travels deeply into the skin causing collagen breakdown, aging of the skin, destruction of vitamin A in the skin, and “indirect DNA damage” (more on this later).

Despite these damaging effects, though, UVA does not cause sunburn. This fact is partly responsible for the lack of standard levels of protection against UVA in sunscreens. The SPF rating you see on packaging is, instead, only a measure of the sunscreen’s effectiveness against UVB.


Though the atmosphere blocks a lot more UVB than it does UVA, it doesn’t eliminate this UV’s dangers. That red, blistered skin you get from lying in the sun too long is proof of this, as it is, effectively, only UVB that causes sunburn.

Staying inside is, of course, the best defense against all forms of ultraviolet radiation, but even if you lived in a greenhouse you’d be ok as far as UVB goes, as it can’t penetrate glass.

UVB, like UVA, is responsible for collagen damage (though at a slower rate than UVA), vitamin A destruction and skin aging, but unlike UVA it causes “direct DNA damage”. On the other hand, we need a certain amount of UVB exposure to enable our bodies to produce vitamin D.


With the shortest wavelength and the greatest amount of energy, UVC is highly dangerous to human beings causing collage damage, skin aging and direct DNA damage. Fortunately, the atmosphere eliminates all UVC so generally it is not a concern for human beings. Manmade sources of it may, however, pose a threat to some occupations if UVC-producing equipment is used incorrectly (pond sterilisation units etc.)

The Effects of Ultraviolet Exposure

Indirect DNA Damage

Indirect DNA damage from ultraviolet radiation occurs when UVA enters the skin and causes the formation of free radicals and reactive oxygen species (ions or very small molecules that are highly reactive). While the DNA itself is not “burnt” in this process, the dangerous molecules that are formed can damage DNA, potentially leading to skin cancer. In fact, nearly all cases of melanoma are attributed to indirect DNA damage.

Direct DNA Damage

When UVB enters the skin and hits DNA, 99.9% of it is converted into harmless heat. The remaining fraction, though, is still enough to damage DNA. This damage manifests as sunburn.

Other Damage

In addition skin damage, UV radiation may also lead to suppression of the immune system and to conditions of the eye, including arc eye, cataracts, pterygium and pinguecula


The brown pigment in the skin is called melanin. When the body is exposed to UV radiation it recognizes the damage that’s being caused and responds by increasing levels of melanin. Melanin absorbs UV radiation, dissipates it as heat and protects the skin from UV damage.

UVA and UVB each bring about increased melanin levels differently. UVA causes the oxidization of melanin already present in the skin, resulting in a quick, short-lasting tan. UVB stimulates the skin to produce more melanin. The tan resulting from this mechanism takes about two days to develop and is longer-lasting.

On the Beach

It’s great to look brown on the beach, but remember just how this happens. It isn’t some sort of summer magic. Tanning is the body’s defense against a form of radiation which, in the case of melanoma, can have potentially deadly effects. Every minute you lie there, soaking up the sun, invisible rays are penetrating your body, causing possibly irreversible damage at a molecular level. Happy sun tanning!

Learn more about the dangers of UV radiation here:

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  1. HotSoup says:

    I’m a fair skinned lad myself and this type of articles are really interesting to read. “Irreversible damage at a molecular level” is enough to scare me of even trying to get some more freckles during summer.
    Thanks for the informative post

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  2. Sundog says:

    It’s really amazing how much the sunscreen industry DOESN’T tell us!

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