* What is UV radiation?

Visible light is only a part of Sun’s light spectrum. Ultra Violet light has shorter wavelength than light of visible spectrum and can not be seen by human eye. UV radiation affects cells producing the skin's pigment (melanosythes). The skin tans when exposed to UV radiation, but in case if it gets too much radiation, but if it gets too much radiation skin may get burnt, developing erythema (reddening) and sunburn. In long-term perspective excessive exposure to the sun may lead to premature skin ageing, development of irregular skin pigmentation, wrinkles and even become a cause for skin cancer.

UV radiation can be categorized into three sections by wavelengths and by the effect they have on human health:

• UVC light – wavelength from 100nm to 290nm;
  UVC wavelength is the shortest of all in UV spectrum and is the most harmful for human health. Fortunately, ozone layer keeps the UVC light off, not allowing it to reach the Earth surface.
• UVB light – wavelength from 290nm to 320nm;
  UVB light is the light that has significant effect on human health as it has the shortest wavelength of all reaching the surface of Earth; UVB light is responsible for sunburns and development of skin cancer.
• UVA light – wavelength from 320nm to 400nm.
  UVA light has the longest wavelength and is the less harmful for human health; although it is under suspicion as a potential cancer-causing agent, it takes hundreds of thousands of times more UVA light than UVB light to achieve the equivalent skin damage.

* UV radiation and Tanning

Tanning is the way for the skin to protect itself from sunburn. Darker pigment is supposed to provide greater protection to the skin, but by the time when tan develops, certain skin damage has already occurred.

Depending on the skin type, people will have different reaction to sun radiation and different tanning patterns, as each skin type has its own self-protection time (period of time when a person can experience direct exposure to the sun with no damage to the skin). If a person needs to stay exposed to the sun for more than term, appropriate skin protection is necessary.

• I Type – the skin always burns, never tans.
  Can remain under the direct sunlight without any protection for 5-10 minutes.
• II Type – the skin normally burns, sometimes tans.
  Can remain under the direct sunlight without any protection for 10-20 minutes.
• III Type - sometimes burns, normally tans.
  Can remain under the direct sunlight without any protection for 20-30 minutes.
• IV Type - rarely burns, always tans.
  Can remain under the direct sunlight without any protection for 40 minutes.

Darker skin responds to tanning better, fair-skinned people have more sensitive skin and tolerate sun exposure poorly, getting rather burned than tanned. Tanning got in solaria doesn’t provide adequate protection to the skin, as it doesn’t cause skin thickening (while the natural sun tan does).

Note: When sunbathing, people should keep in mind that the amount of UV radiation they get can be increased if it gets reflected from nearby surfaces. Especially good reflectors are white sand (reflects 20% of UV rays) and snow (over 80%). Even when the weather is cloudy, people still get 90% of UV radiation transmitted through a thin cloud layer and may get tanned and even burned. People, who prefer sunbathing keeping a horizontal position, receive 4 times more radiation than those who prefer sunbathing while standing or walking.

* Skin Protection

Excessive or prolonged UV radiation contributes to premature skin ageing - skin becomes dry, coarse and irregular pigmentation gets developed. Besides that, it is suggested that frequent excessive sun exposure and sunburns, especially in childhood, increase the risk of melanoma (type of skin cancer which is very dangerous, as it metastasizes to other parts of body).

It is important to remember that sun protection should be a part of all summer and winter activities. Sunscreen lotions provide this protection, preventing the skin from being burned. Sunscreens provide a barrier between the skin and the sun (physical, chemical or both), which can either absorb or reflect specific wavelengths of the sun's spectrum.

Note: The SPF (Sun Protection Factor) indicates the time person can stay in the sun after the sunscreen is applied. This time depends on the self-protection time of your skin, i.e. if you have the 1st type of the skin (see the list of skin types above), self-protection time for your skin is 10 minutes and the SPF of your sunscreen is 6, you can stay in the sun for a maximum of 60 minutes.

However, it is important to remember that sunscreen must be regularly reapplied, because clothes friction, perspiration and so on strip it off throughout the day.

* Vitamin D

In order to remain healthy, human organism needs to get adequate amounts of vitamin D, which regulates the calcium and phosphorus levels in the blood by promoting their absorption from food in the intestines, and by promoting re-absorption of calcium in the kidneys, which enables normal mineralization of bone and is also needed for bone growth and remodeling. Research studies also suggest that getting enough vitamin D in childhood may help prevent multiple sclerosis in adulthood.

Note: Most people know that vitamin D gets produced in the skin when it is exposed to UVB rays in sunlight, and there are many people who proclaim that sunscreens don’t allow the skin to get enough of Vitamin D, causing its deficiency. But not all of them know that adequate amounts of vitamin D3 can be made in the skin after only ten to fifteen minutes of sun exposure to the face, arms, hands, or back without sunscreen at least twice a week. With longer exposure to UVB rays, equilibrium is achieved in the skin, and the vitamin simply degrades as fast as it is generated.