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Chemistry LibreTexts

5.5: The Basics of Skin Cancer

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  • Exposure to Ultraviolet Radiation

    Of all the types of ionizing radiation, people come into more contact with ultraviolet radiation. Sources of this radiation would include the sun, ultraviolet lights, and tanning beds. The sun produces three different forms of ultraviolet rays (UVA, UVB and UVC). Fortunately, the deadliest of these three rays (UVC) never reaches the earth's surface and is absorbed by Earths' ozone layer. However, both UVA and UVB reach the Earth's surface to affect living systems.

    Figure \(\PageIndex{1}\): Effect of Light on skin

    UVA is produced naturally by the sun and artificially by lamps and tanning beds. For years, sunbathers believed that UVA provided only a youthful glow. Now, the American Academy of Dermatologists has condemned the use of tanning beds. Scientific research has correlated certain types of skin cancers (mainly basal and squamous cell) with the use of these devices. Besides skin cancer, tanning beds cause premature aging and damage to your eyes. If a tanning bed is not properly sanitized between uses, skin diseases can be transmitted from one consumer to another.

    Recognizing Suspicious Skin Changes

    According to the American Academy of Dermatologists, skin cancer is the most common form of cancer. Exposure to ultraviolet rays or arsenic can cause skin diseases. Additionally, some individuals may be genetically predisposed to developing this illness (check out your family tree). Approximately 10,000 Americans a day will be diagnosed with one of the three different forms of skin cancer. Millions of Americans have already been diagnosed with the most common form of skin cancer, basal cell carcinoma. This type of cancer grows very slowly and can spread to other parts of the body. Basal cell carcinoma frequently appears on the head and neck of a patient. Rarely, basal cell carcinoma can eventually affect other areas of the body like skin or bone.

    Figure \(\PageIndex{2}\): ABCDEs of Skin Cancer. A brown spot on the skin is likely to be a harmless mole, but it could be a sign of skin cancer. Unlike moles, skin cancers are generally asymmetrical, have irregular borders, may be very dark in color, and may have a relatively great diameter.

    Squamous cell carcinoma appears more commonly on the face, neck, lips and hands of person. For females, squamous typically presents on the lower leg portion. This form of skin cancer is more likely to metastasize (spread) than basal cell carcinoma. If caught early and treated, patients can easily survive both basal and squamous cell carcinomas.

    Melanoma, the most serious form of skin cancer, is the least common of all skin cancers. This type of cancer usually manifests on the trunks of males and the legs of females. It can spread easily to the brain, liver, bones, abdomen, or lymph notes. If detected early, survival rates are good and life expectancy will be normal.

    Figure \(\PageIndex{2}\) compares normal pigmentations to moles that have changed into melanoma. Monthly reviews of skin lesions and seeking medical advice is key in surviving this disease. Be sure to note these visual characteristics (the ABCDE's) of skin cancer for future evaluations (life and class).

    Sunblocks and Sunscreens

    UVB radiation in sunlight allows the skin to produce vitamin D. This vitamin prevents bone disorders like rickets and osteoporosis (brittle bone disease). The American Academy of Dermatology suggests vitamin D be obtained through foods or nutritional supplements. Excessive exposure to UV can be damaging and the pigment melanin, deposited in cells at the base of the epidermis, helps to protect the underlying layers of the skin from this damage. Melanin also colors the skin and variations in the amount of melanin produces colors from pale yellow to black. The darker the skin tone, the more melanin one has, and the less likely skin cancer will occur.

    Figure \(\PageIndex{3}\): The author's great, great- grandmother was diagnosed with skin cancer on her nose during the 1950's.

    Excess exposure to the sun can cause sunburn. This is common in humans, but light skinned animals like cats and pigs can also be sunburned, especially on the ears. Skin cancer can also result from excessive exposure to the sun. As holes in the ozone layer increase exposure to the sun’s UV rays, so too does the rate of skin cancer in humans and animals.

    Sunscreens and sunblocks are designed to protect skin from ultraviolet rays. Sunblocks contain inorganic ingredients like zinc oxide or titanium dioxide. These chemicals act as UV filters by reflecting the sun's UV rays. Sunblocks can have grainy textures due to the inorganic components. The thick nature of a sunblock can make it difficult to spread evenly on the skin. Sunscreens contain organic compounds like oxybenzone, avobenzone, homosalate, and octinoxate (Figure \(\PageIndex{4}\)). By absorbing ultraviolet rays, these compounds decompose and give off heat. Sunscreens apply smoother than sunblocks. Often, manufacturers will combine sunscreen and sunblock ingredients to make their products.

    Figure \(\PageIndex{4}\): Effect of Light on skin

    Sun protection factor (SPF) measures a product's protection from UVB rays. SPF does not quantify protection from UVA radiation. The American Academy of Dermatology recommends you select a sunscreen or sunblock with a minimum SPF factor of 30. This SPF value means a lotion can filter out 97% of UVB rays. Moving to a SPF of 50 will only filter out 1 more percentage of UVB rays. Increasing a SPF factor past 30 really does very little in shielding skin from UVB radiation.

    Products that protect skin from UVA must be labeled as being broad spectrum. Sunblocks provide UVA and UVB protection, but sunscreens can vary on what they can screen. Every two hours, sunscreens/sunblocks should be reapplied to the skin. Sweating and swimming can remove sunscreen/sunblock products. No sun products are waterproof, but some are labeled as being water resistant. Consumers are encouraged to reapply these products every two hours as well.

    Clothing and Other Products (need student writer?)

    UPF-Ultraviolet protection factor for clothing.  Blocks UVA and UVB (unlike SPF notation).  Want:  dark, loose, polyesters, silk.  Skin Cancer Foundation Seal of Excellent Approval (UPF = 50, blocks 98% of UVA and UVB). Hats etc.


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