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D. Coping with the Sun on Mount Everest
Mount Everest is an environment of extremes in all weather conditions, but this is especially evident in temperature and UV (ultraviolet) exposure. Both temperature and UV problems on Mount Everest are a function of the physical environment (especially snow) and the high altitude. Temperatures can reach as high as 41 degrees Celsius as the sun's rays pierce the thin atmosphere found at this elevation and are reflected by the snow.

As a result of the high altitude, temperatures can also get as low as minus 46 degrees Celsius on the upper parts of the mountain (the troposphere decreases in temperature with height), but the sun's rays are even more of a danger at this altitude despite the cold.

WHY?
At sea level and elevations much lower than that of Mount Everest, only 47 per cent of the energy from the sun hits the ground. The atmosphere absorbs the other 53 per cent or it gets reflected back into space. Then the heat is distributed through the air by convection. Note: The amount of heat in a region of the earth is determined by its proximity to or from the equator (see Section A, Climate and Weather).

 

The fate of solar radiation From "Ultimate Visual Dictionary of Science," Stoddart 1998.

Since Mount Everest is 8,050 metres (29,035 feet) high, it is in the uppermost part of the troposphere layer of the atmosphere that helps to protect the Earth from the sun's UV rays.

This means that a large percentage of the harmful rays that are filtered out gradually through the atmosphere at lower altitudes (where most people live) are not filtered on Everest. Climbers at this height are exposed to very dangerous levels of ultraviolet radiation.

Also, 85 per cent of UV rays that do reach Earth (of which most are absorbed at lower altitudes) are reflected off the fresh, white snow, almost doubling the radiation exposure in this environment (Canadian Dermatology Association, Sun Facts).

The sun's UV rays have the potential to be extremely dangerous for high altitude climbers, as well as for those people who live at relatively high altitudes on a year-round basis such as the Sheraps in the Mount Everest area of Nepal. Even more alarming is how little exposure is required to cause serious damage in a very short time.

New research from the American Academy of Dermatology (AAD) can be interpreted to show that UVB levels are 29 times more intense at the summit of Mount Everest than they are at sea level. This means that a climber with an average complexion (neither extremely light nor dark) would develop serious sunburn in less than six minutes. In fact, the research says that the same person would sunburn after six minutes at only 11,000 feet (3,353 metres) compared to 25 minutes at sea level. These numbers are based on a clear day at noon in either location, with no UV protection such as sun block or protective clothing.

You can read more about this research from the American Academy of Dermatology.

With this kind of information, it is easy to see why climbers have to protect their skin from the sun's rays and the glare from the snow, which increases the intensity of the UV rays. This is just as important as protecting themselves from the extreme cold to avoid serious skin damage. With the sun there is the added danger of increasing your chance of developing skin cancer (Melanoma).

People who live in higher altitudes and in areas where the ozone layer is thinning need to be educated by their local health organizations and governments to protect themselves from the sun more carefully. There is a major education program being conducted by the government of Australia, since its population of citizens has had dramatic increases in rates of skin cancer in recent history.

This is due to a large number of fair complexions in an area that has the highest levels of solar radiation on earth.

Also, human pollutants to the environment are damaging the ozone layer. There are places in the ozone layer that are either disappearing or thinning at an alarming rate, which is leading to compounding rates of skin cancer as a result of more UV rays (particularly more UVB) passing through the atmosphere to Earth. People burn faster than they did before with the same amount of sun exposure time.

The best ways to avoid skin damage and reduce the risk of developing skin cancer include the following suggestions by doctors:
(source: United States Environmental Protection Agency)

• Minimize exposure at midday (10 am to 3 pm).
• Apply a sunscreen with SPF-15 or higher to all exposed areas especially after swimming, perspiring or spending time in the sun, even on cloudy days.
• Apply sunscreen every two hours.
• Wear clothing that covers your body and shades your face and neck.
• Avoid unnecessary exposure to radiation from sun tanning, sunlamps or tanning parlors.
• Protect children by keeping them from excessive sun during the hours of strongest sunlight, by applying sunscreen liberally, and frequently to children older than six months of age.

What is the difference between UVA and UVB radiation?
There are actually various types of radiation emitted from the sun, including visible light and infrared radiation, but it is ultra violet radiation that most affects our skin and eyes. In addition to UVA and UVB rays there are UVC rays. UVC rays are stronger than UVA and B, but they are filtered out by the ozone layer of the stratosphere and do not reach the earth.

UVB (ultraviolet B) - is responsible for sun burns, delayed tanning (the process continues in the skin after sun exposure is ended), aging, cataracts of the eye, and genetic damage that can lead to skin cancer. UVB rays are short wave radiation. They are the most powerful and potentially harmful, even though much of UVB is filtered out by the ozone layer in the stratosphere. The closer you live to the equator, or the higher the elevation, the more intense exposure is received. Other indicators for intensity of UVB exposure are time of day, season (winter has less direct sunlight) and cloud cover (dense, dark cloud cover does filter UV, though haze and light clouds do not).

UVA (ultraviolet A) - causes immediate tanning and contributes to premature aging and possibly skin cancer. There are no regulations for UVA protection in sun block creams and lotions. The one to 15 ratings (and higher) indicate the level of protection from UVB. UVA rays pass through the ozone layer and until recently were considered to be harmless. The current status of this information is due to relatively recent studies. The waves of this radiation are longer than UVB and the exposure is virtually the same all year.

Why does the sun affect our skin the way it does - with suntans and sunburns?
First of all, we have to know something about our skin. Skin is one of the body's organs - the largest one in fact. It has cells and tissues that perform a specific function of protecting the body.

 

Web Links How Sunburns and Suntans Work SunSmart Sports DermNet American Academy of Dermatology Also, direct inquiries to: Environment Canada (or similar government departments in other countries) Canadian Dermatology Association (or similar organization in your country) Canadian Cancer Society

It is made up of two main layers (with other layers within them), the outside layer being the epidermis and the inside layer being the dermis. Skin has many sensors, which makes it sensitive to heat, cold, pressure, itching and pain. Being sensitive is good for us because it warns us when something is damaging our skin.

The part of the skin that we can see on the outside of our body is only the first of many layers of our skin organ. In fact, all we see is the layer of dead cells that make up the stratum corneum layer of the epidermis (or the outside part of our skin).

The part of your skin that is responsible for the development of a suntan (or burn) is the malpighian layer of the epidermis. The epidermis has several layers within it. On the outside is the layer of dead skin cells that we see called the stratum corneum - what we call our skin. Then comes the malpighian layer, which contains the granular layer, the spinous layer and the basal layer.

The basal layer of the epidermis is the last layer before the dermis layer. The basal layer contains melanocyte cells that produce melanin - the pigment that reacts to the sun to create a tan, and they are the cells that are responsible for melanoma, a form of cancer associated with sun exposure on the skin. All people have approximately the same number of melanocytes; the difference in the color of our skin is determined by how much melanin they produce.

What causes tans?
Upon exposure to sunlight, melanocytes increase in activity as a reaction to the UV rays from the sun to produce tanning. They produce more melanin pigment, which causes the darker appearance of the skin.

Actually very brief exposure to sun for Caucasians builds protective melanin in your skin. Production of melanin takes quite a long time, but the brief exposure to UV rays is enough to stimulate the melanocytes into production of melanin which continues even after coming in from the sun. If you expose yourself very briefly to the sun for five to seven days, Caucasians can build pigment levels that are protective.

The same cautious approach is not as necessary for races with dark skin since their skin produces melanin on a continuous basis, which provides more protection from UV radiation of the sun. This information however is only related to short exposure and as one of the ways to prevent burning. Any exposure to the sun, especially during 11 am and 4 pm will contribute to aging effects of the sun, particularly with prolonged exposure without proper protection including appropriate clothing and sunscreen.

What causes burns?
We recognize sunburn as red, painful skin that can have blisters in very extreme cases. It occurs after long term exposure to the sun without proper protection (the actual damaging amount of time depends on your natural skin pigmentation - whether it is light or dark). We often say, "I didn't really realize I was getting burned until after I came inside". This is because burns are caused by UVB rays which are responsible for delayed tanning and sunburn in severe cases.

When you get a sunburn you are experiencing damage at the cellular level. In reaction to this damage, the body increases blood flow to the skin to help repair the damage. The increased blood flow is the source of the redness and causes extra blood in the upper layers of your skin.

What causes melanoma or skin cancer?
Melanoma is caused by UV radiation damage to the melanocyte cells. Repeated exposure and damage caused by UV radiation can cause cancerous mutations of the cells.

There are three main forms of skin cancer. They are:

• Basal Cell Carcinoma (most common)
• Squamous Cell Carcinoma (second most common)
• Malignant Melanoma (deadliest form requiring early detection)

How do sun blocks and sun screens work?
Sunscreen filters UV light. Sun block absorbs or reflects UV light.

The sun protection factor (SPF ratings) found on sunscreen and sun block creams and lotions indicates the product's ability to block UVB rays. Dermatologists advise that you choose a SPF factor of at least 15, regardless of your skin type. If you are very fair, you should seek higher SPF levels.

For protection from UVA in your sunscreen, look for the term "broad spectrum protection". The product should also be approved by your national dermatology association. You may also contact your dermatology association for a list of approved sunscreens.

Ingredients to look for are:

Melanin - some producers are adding this to sunscreen, so that, just like the body, it will absorb the UV light, therefore blocking the skin from the UV.

PABA (para-aminobenzoic acid) - is being used less in products now because of the high instances of allergic reactions. PABA filters UVB light.

Titanium dioxide - blocks UVA and UVB. This is the type recommended for sensitive skin and high altitude exposure as a complete blocker of sunlight for the skin. A Calgary dermatologist has recommended the team use brands which are chemical free, meaning that they do not have a lot of other ingredients like moisturizers, etc. They are strictly used for the purpose of blocking the ultraviolet rays.

Don't we need the sun's ultraviolet rays for vitamins?
Yes, humans do need Vitamin D to metabolize calcium. We can get that from ultraviolet light, which converts 7-dehydrocholesterol in your bloodstream into Vitamin D. However, we also have Vitamin D fortified milk and in the past, we took cod liver oil. For more details, please see the "How Vitamin D Works" section of How sunburns and suntans work.