The Danger of Ultraviolet Rays

Ultraviolet rays are divided into three separate categories and have different effects upon our bodies. Those three are: UVA, UVB and UVC rays- often written as UVA, UVB, and UVC. There are varying theories about UV radiation, but most experts agree that only type UVA and UVB rays can reach the Earth and are, therefore, harmful to our skin. UVC rays, while also dangerous, cannot get through the ozone layer to the Earth.

The UVB rays, often referred to as the tanning rays, are responsible for most cases of sunburn; UVB rays are absorbed by the very top layer of the epidermis surface. This layer is about as thick as a silk scarf and so the UVB rays penetrate the skin easily and activate cells called melanocytes (cells in the skin that give its pigment). Melanocytes, in turn, produce the pigment melanin giving you a tan. As UVB rays are much shorter than UVA rays, they are more prevalent during the summer when the Sun is closest to the Earth.

The UVA rays, as they are much longer than UVB rays, go deeper into the skin. UVA rays are less likely than UVB rays to cause sunburn, but they are considered the main cause for age spots, the loss of the skin’s elasticity and wrinkling- thus leading to the premature aging of the skin. More seriously, UVA rays are the chief suspect in skin cancer. One reason UVA rays are more dangerous is that they are potent all year round. If you want to see the effects of UVA rays, place a colored object by a window and watch how the colors fade over a few months.

Exposure to both UVA and UVB can lead to skin cancer, which in turn can be benign or malignant. Research shows that UVA not only increases UVB's cancer-causing effects, but may directly cause some skin cancers, including melanomas.

Malignant cancer appears as a consequence of abnormal multiplication of skin cells. The uncontrollable growing of these cells leads to a (in most cases) lethal melanoma tumor. Melanoma begins as a dark skin lesion and may spread rapidly to other areas on the skin and within the body. If you notice a discoloration on your skin, check with your doctor. If melanoma is caught early, it can be treated.

Benign skin cancers are not that dangerous, but they should be treated so as to stop a tumor’s growth. Those most likely to get skin cancer are fair-skinned people who also burn easily in the Sun. Non-tumor cancers are generally limited to the surface of the skin and almost always are the result of UVB exposure.

In addition to causing cancer, excess exposure to UV rays may also lead to the weakening of the immune system. UV radiation alters the distribution and function of white blood cells which are responding to the “injury” of being overly exposed to the sun. Tanning is the skin’s reaction to an injury.

UV index

Now that you know how dangerous UV rays can be, you need to know how strong those rays are on any given day. The UV index is especially useful if you are not using sunscreen or taking other precautions on a regular basis; when the UV index is high, you should know that not taking precautions could be detrimental.

The UV index is an international standard measurement of how strong the UV rays are at a particular place on a particular day. It is a scale primarily aimed at the general public and used in daily weather forecasts.

The purpose of the index is to help people to effectively protect themselves from UV rays, and thereby avoid sunburns, eye problems (such as cataracts), skin aging and skin cancer. When the UV index is 3 or higher, public health organizations recommend that people protect themselves by putting on sunscreen and wearing a hat. Following is a chart of UV index values and the exposure categories:

UV Index ValuesExposure Categories
0 - 2Minimal - Wearing a hat will give enough protection.
3 - 4Low - Wearing a hat and applying a sunscreen with SPF 15 is advised.
5 - 6Moderate - Wearing a hat, applying a sunscreen with SPF 15 and remaining in the shade is advised.
7 - 9High - In addition to above-mentioned precautions, it is recommended to stay indoors between 10 a.m. and 4 p.m.
10 +Very High - In addition to the above-mentioned recommendations, you should stay indoors if at all possible.


UV IndexCategorySunburn Time
over 9extremeless than 15 minutes
7-9highabout 20 minutes
4-7mediumabout 30 minutes
0-4lowmore than 1 hour
When the UV index is over 9, UVB is extremely strong, and you will burn in less than 15 minutes.

It’s important to keep in mind that UV index data has important limitations. Mainly, the UV index concentrates more heavily on UVB frequencies and tends to underestimate UVA exposure. This means the UV index is more useful in assessing the risk of sunburn than in assessing long-term damage to the skin which subsequently leads to wrinkles and age spots and other aging signs. Therefore, while the recommendations above are certainly helpful, if you are interested in long-term anti-aging skin care, you may consider being more diligent in your sun protection regimen regardless of the UV index.

Additionally, all UV radiation is not created equal. There are some factors which affect their levels such as:

  • Latitude: The closer you get to the equator, the higher the UV radiation levels will be.
  • Sun elevation: As the sun climbs higher into the sky, UV radiation also intensifies. That means UV radiation levels are highest around noontime and in the summer
  • Time of the day: According to research, the hours of 10am to 4pm is the most dangerous period for UV radiation- it’s purported that as much as 60% of the day’s radiation comes between those times.
  • Time of the year: In most countries, UV radiation levels are usually many times higher in summer than in winter. When summer is at its peak, you can burn in 15 minutes or less. The months from May to September seem to pose the greatest risk for UV rays.
  • Cloud cover: UV rays can penetrate through clouds, and so there is still a need to protect yourself if you are going outside. In fact a lightly cloudy day can contain the same amount of UV radiation as a clear day. Of course, the heavier the clouds, the more UV radiation will be blocked.
  • Altitude: The higher you go, the more chance you have of being exposed to UV radiation. As the atmosphere becomes thinner, much less of the UV rays are being filtered out. So, for example, at an altitude of 20,000 feet, UV rays can be up to 30% higher than those found at sea level.
  • Ground reflection: dirt, water and foliage (grass, for example) reflect less than 10% of UV rays; snow can reflect as much as 80%; beach sand about 15% and the foam found on the sea about 25%.

The Effect of Reflected or Indirect Sunlight

Studies show that reflected sunlight may retain over a third of its UV rays. That means sunlight reflected off of sand, water, snow and even clouds can be full of dangerous UV rays. Certainly the intensity of the UV rays is reduced by these reflectors- but only by 20 – 40 percent.

The Prevalence and Danger of Indoor UV light

It has been said that glass blocks UV rays. It does block UVB quite well but often fails to block much of UVA. (Remember the colored object example given above?) The degree of indoor UV exposure depends on light intensity, type of glass and other factors. For example if the glass is clear, 75% of UVA can pass through it. If the glass it tinted or reflective, it absorbs more of the UVA but still allows about 25-50% to pass through.

There is laminated glass and UV-blocking coated glass also on the market. They both filter out from 95 to 99% of all UV light. However, neither is commonly used in residents or in businesses- that is, they are used only in special circumstances. It’s safe to go under the assumption that UV rays are coming in through your windows and therefore you should protect yourself accordingly.

It’s common knowledge that sun damage is the number one factor in skin cancer and in the aging of the skin. In fact, in the three decades from 1973 to 2003, the incidence of melanoma, the deadliest skin cancer, rose by 81 percent.
During peak sun hours use window blinds or shades to block out direct exposure. If you can, try to arrange your workspace and sitting areas not to be too close to the windows. These areas will best serve you away from direct sunlight. As you get further away from a window, UVA rays decrease significantly. Therefore, it makes the most sense to avoid spending too much time close to the windows- especially if you have large windows.
Sunscreens come in creams, sprays, gels, lotions, sticks, and ointments. Although a higher SPF number provides better protection, it does not necessarily increase the length of time you can be exposed to the sun.
The first step in finding and choosing the best sunscreen for you is to choose a product that blocks both UVA and UVB rays. That is, the better the sunblock, the stronger its ability to provide you with a high degree of protection against sunburn, skin aging, and skin cancer.
In the previous sections, the dangers of UV radiation exposure have been clearly explained and expounded upon. However, total avoidance of the sun can also lead to negative consequences. That is, there are health benefits to be had from exposure to sunlight.