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เป็นที่ทราบกันว่าแสงแดดมีประโยชน์ต่อการดำรงอยู่ของโลกมนุษย์อย่างมาก ในแง่ของสุขภาพของมนุษย์เองก็มีประโยชน์ในการรักษาโรคหลายชนิดทั้งทางร่างกาย และจิตใจ อย่างไรก็ตาม การใช้เวลาในที่กลางแจ้งนานเกินไปโดยไม่ได้ป้องกันก็เป็นโทษเช่นกัน ได้แก่ การเสื่อมสภาพของผิวหนัง ผิวตกกระ ฝ้า เพิ่มความเสี่ยงของมะเร็งผิวหนัง บทความนี้จึงเสนอข้อควรรู้เกี่ยวกับแสงแดดที่ท่านควรทราบ เพื่อจะได้หาทางป้องกันได้ถูกวิธี
ท่านทราบหรือไม่ว่า แสงแดดที่คนเรามองเห็นเป็นสีต่างๆ เป็นแค่ส่วนหนึ่งเพียงน้อยนิดของรังสีในแสงแดดที่ส่งมาจากดวงอาทิตย์ แสงแดดมีคุณสมบัติเป็นคลื่น จึงแยกรังสีออกเป็นช่วงๆตามความยาวคลื่น ( Wavelength ) รังสีชนิดหนึ่งที่เรียกว่า อัลตร้าไวโอเล็ต ( Ultraviolet, UV มีความยาวคลื่นสั้น ) เป็นรังสีที่ทำให้เกิดการเปลี่ยนแปลงของผิว คือ ทำให้เป็นสีแทน ทำให้ผิวไหม้ มีอยู่ประมาณ 6% ของรังสีจากดวงอาทิตย์ที่ส่องกระทบผิวโลก ส่วนที่เหลือคือ รังสีที่ตาคนมองเห็นมี 48 % นอกนั้น 46% เป็นรังสีที่มีความยาวคลื่นมาก
Besides emitting light rays that we can see, the sun sends out ultraviolet rays that are invisible. The ultraviolet (UV) rays can cause suntans and sunburns. About 6% of the solar radiation that reaches the earth's surface is ultraviolet radiation (very short wavelengths), 48% is visible light and 46% infrared light.
The total amount of harmful UV radiation that reaches the skin at any given time is influenced by such factors as season, time of day, conditions of the earth's atmosphere, and proximity to the equator where the amount of UV light is the greatest. For example, sun worshipers soak up more ultraviolet rays per hour in Florida than they would in Maine because the South, which is closer to the equator, receives 1 1/2 times as much of the sun's rays as does the North.
Your chances of developing a sunburn are greatest between 10 AM and 3 PM when the sun's rays are strongest at all latitudes. The risk drops considerably before and after those times.
Most people discount the risk of getting a sunburn on a cloudy or overcast day when the sun is not shining brightly. However, on these foggy, cloudy, or slightly overcast days, a sunburn can be induced when sunlight is scattered by atmospheric conditions. Up to 80% of UV rays can "penetrate" through the clouds. However, by absorbing harmful rays, atmosphere pollutants such as dust, smoke, and dirt offer partial protection against the risk of sunburn.
Though clothing generally absorbs or reflects UV rays, white fabric like that used in shirts as well as wet clothes that cling to a person's skin can transmit a large amount of UV light.
Beach umbrellas do not provide full protection because UV rays can still bounce off sand, water, and porch decks to the person lounging underneath. Snow reflects up to 80% of the sun's rays. Knowing that shiny surfaces reflect the sun's rays, some people use sun reflectors to increase their exposure to the sun and thereby increase their tans. This is a dangerous practice because delicate areas, like the eyelids, ears, and under the chin, can be burned severely.
It is easier to burn more severely on a hot day because the heat increases the effects of ultraviolet radiation. And it is easier to burn at high altitudes and in the mountains because there is less atmosphere to block ultraviolet rays. Wind tends to increase the ill effects of the sun's rays.
If you are exposed to the sun too long, you may develop a mild redness within a few hours. This usually peaks within 24 hours. A severe reaction which is marked by extreme tenderness, pain, swelling, and blistering, may be accompanied by fever, chills, nausea, and delirium within 12 hours of the overexposure. Unfortunately, there is no quick cure--despite claims from some sun cream manufacturers--for the discomforts of an acute sunburn. Home remedies, like wet compresses, tub baths, and soothing lotions, usually provide partial relief. If you develop a severe burn, consult your dermatologist who may suggest special ointments or drugs to reduce swelling, pain, and prevent infection.
A sunbather views a tan as a symbol of good health and looks. However, physicians consider tanning a response to injury because the sun kills some cells on contact and injures others. Tanning occurs when the UV rays penetrate through to the skin's inner layer to produce more melanin, which then moves toward the outer layers and becomes visible as a tan. Melanin production usually occurs 48 hours after the initial sun exposure, peaking about two weeks later.
Wrinkling of the skin from years of sun exposure
People who work or bask in the sun for years without sunscreen protection usually develop a tough, leathery skin that may make them look 15-to-20 years older. Chronic exposure, starting in childhood, typically results in a change in the skin's texture. This leads to excessive wrinkles and variable degrees of skin thickening and thinning. After years of excessive exposure, the sun weakens the skin's elasticity, leaving the appearance of sagging cheeks and deeper than normal facial wrinkles. In addition to the other harmful effects on the skin, the sun can cause discoloration--red, yellow, gray, or brown blotches, formation of "liver spots," and gray scaly growths called actinic keratoses which may develop into cancer. It should be emphasized that these changes are not just due to recent exposure, but to cumulative effects throughout life. Attention should be paid to the protection of children who tend to have longer outdoor exposure and may not show the effects of sun damage until later in life.
Skin cancer is a disease caused by excessive and long-term exposure to the sun, according to scientific studies. It rarely occurs in the occasional sunbather. More than 90% of all skin cancers occur on parts of the body exposed to the sun's radiation. The face, neck, ears, forearms, and hands are the most common locations.
Basal cell carcinoma (left) and Malignant Melanoma
(right)
The three main types of skin cancer are basal cell, squamous cell, and melanoma.
Basal cell carcinoma usually occurs in persons who have light hair and fair complexions, who sunburn readily, and who do not tan. Appearing as a small, shiny, fleshy nodule on exposed parts of the body, basal cell carcinoma grows slowly. When diagnosed and treated promptly, it has a high cure rate.
Squamous cell carcinoma, which typically develops on the face, ears, lips, and mouth of fair-skinned persons, usually starts out as a red, scaly, plate-like patch or nodule. Though it can spread to other parts of the body, it also carries a high cure rate when detected and treated early.
Melanoma, the most dangerous form of skin cancer, usually shows up as a dark brown or black mole-like lesion with irregular edges. Sometimes, the growths may turn red, blue, and white. The most common sites are the upper back in men and women and the chest and lower legs of women.
Photoallergic dermatitis
Some people develop allergic reactions to sun exposure. These reactions occur after only short periods of exposure. Bumps, hives, blisters, or red blotchy areas may occur repeatedly in the same place after each sun exposure. Researchers say these reactions are due to a person's previous sensitization to sunlight or to contact with certain cosmetics, perfumes, plants, topical medications, or sun preparations. Some drugs, including birth control pills, antibiotics, antibacterial ingredients in medicated soaps and creams, and tranquilizers can make some individuals more sensitive to the sun, causing a skin eruption. The allergic reaction is called a photosensitivity reaction. If this occurs see a dermatologist and avoid the offending product in the future.
Some diseases become worse or begin upon exposure to the sun. These include herpes simplex (cold sores), chickenpox, a number of less common disorders, serious skin diseases, conditions that affect the body's metabolism, and genetic problems. In lupus erythematosus, overexposure to the sun may lead to a very serious attack and even death if unrecognized or inappropriately treated.
Whether individuals burn or tan depends on a number of factors, including their skin type, the time of year, and the amount of sun exposure they have received recently. The skin's susceptibility to burning has been classified on a five-point scale as follows:
Tanning should be discouraged but some individuals will seek a tan despite warnings. The safest way to tan is to do it gradually and to use an appropriate sunscreen with an SPF of 15 or greater one half hour before sun exposure.
Gradual exposure permits optimal production of the browning pigment, melanin, to take effect. This protects somewhat against sunburn also. Gradual exposure also helps to thicken the outer layer of the skin. That, in turn, serves to protect the easily damaged skin layers from harmful sun rays.
Children should be protected from the sun's rays at an early age. Most damaging exposure to sunlight occurs before the age of 20.
The three best ways to prevent sunburns are to avoid the sun during the peak hours of solar radiation, to use sunscreen or sunblock preparations, and to wear loose clothing. Besides protecting from overexposure to sunlight, sunscreens help to prevent other sunrelated problems, like aging skin and precancerous growths. Classified as "drugs" by the United States Food and Drug Administration, sunscreens come in the form of ointments, creams, gels, and lotions. They are rated according to their effectiveness in blocking out sunburn rays, with higher numbers indicating more blocking action.
Individuals should select a sunscreen to provide protection according to their particular skin type, the time of year, their location, and the activities they plan to do. People with fair skin who burn easily and tan poorly (Types I & II) should use a product with an SPF value of 15 or greater. Individuals with less sensitivity can use sunscreens with lower numbers (i.e. 8-15) when exposed to the sun.
Sunscreens protect the skin from burning rays
Though the newer sunscreens are more resistant to loss through perspiration and removal by water, they still should be reapplied frequently during peak sun hours or after swimming. To prevent streaks of tan, spread on an adequate amount of cream evenly on the areas that will be exposed. The sunscreens work by absorbing, reflecting, and scattering the sun's rays on the skin. Some sun preparations contain the following chemicals: paraaminobenzoic acid (PABA) and/or PABA esters and/or padimate-O. Some people are allergic to PABA-based sunscreens and use of the following type of ingredients may be substituted: benzophenones (oxybenzone and sulisobenzone), cinnamates (octylmethyl cinnamate and cinoxate), and salicylates (homomenthyl salicylate). Cosmetics and lip protectors which contain these chemicals are also on the market.
People who are out in the sun a lot, like lifeguards, and people with extreme sun sensitivity should apply an opaque sunscreen--such as zinc oxide, a thick white ointment--to completely cover vulnerable spots like noses and lips.
Individuals should select a sunscreen to provide protection according to their particular skin type, the time of year, their location, and the activities they plan to do, but always should use a product with an SPF value of 15 or greater.
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