It's very tempting to lie out in the sun, to soak up the warmth, to work on a tan. I know my first instinct when I reach the warmth of the tropics is to strip down to my swim trunks, put on my sunglasses and begin to soak up the rays. Unfortunately, that's not a good thing to do. What I ought to do is coat my exposed skin with sunscreen, put on a broad-brimmed hat and try to protect myself as much as possible from the relentless ultraviolet radiation. For thousands of years, until modern times, sunbathing and a suntan have been associated with good health. That concept has never been proven. In fact, although pale, untanned skin may not appear as "healthy" as a bronzed look, it's healthier. I can't begin to count the number of people who have had a dive trip ruined because of a sunburn, which can be sufficiently severe to cause a victim to be laid up for days. Remember, it's a burn, and it can be just as bad as getting caught in a fire.
Solar radiation that strikes the Earth includes 50 percent visible light (wavelength 400 to 800 nanometers), 40 percent infrared (1,300 to 1,700 nm), and 10 percent ultraviolet (UV — 10 to 400 nm). Sunburn is a photosensitivity reaction caused by exposure of the skin to ultraviolet radiation (UVR) from the sun. UVA is 320 to 400 nm, UVB is 290 to 320 nm and UVC is 100 to 290 nm. UVC is filtered out by the ozone (a tri-atomic form of oxygen) layer of the atmosphere. UVB is the culprit in the creation of sunburn. UVA is of less immediate danger, but is a serious cause of skin aging, drug-related photosensitivity and skin cancer.
Ultraviolet exposure has many variables: the time of day (greatest between 9 a.m. and 3 p.m.), season (greater in the summer), altitude (there is a 4- to 6-percent increase per each 1,000 feet/304 m of elevation above sea level), location (greater near the equator) and weather (greater in the wind).
Divers are at particular risk for sunburn because water may reflect 10 to 100 percent of UVR, depending upon the time of day, location and surface. ("Flat" is more reflective than "chop.") Most clothes reflect (light-colored) or absorb (dark-colored) UVR. However, it is important to note that wet cotton of any color probably transmits considerable UVR, so snorkeling in a plain white T-shirt may provide very little protection from the sun.
Skin darkening occurs immediately upon UVA exposure, as melanin (pigment) already present in the skin is released. This effect only lasts for 15 to 30 minutes. Tanning occurs after a minimum of three days of exposure, as additional melanin is produced. If the skin is not conditioned with gradual doses of UVR (tanning), a burn can be created.
A person's sensitivity to UVR depends on his or her skin type and thickness, pigment in the skin and weather conditions. (See the sidebar "Sun-Reactive Skin Types.") Well-hydrated thetic sprays, many of which contain benzocaine, should be avoided, as they can occasionally cause sensitization and an allergic reaction. Menthol-containing lotions may be helpful. Topical steroids do not diminish sunburn.
If the victim is deep-red in color without blisters (first-degree burn), a stronger anti-inflammatory drug, such as ibuprofen, may be given. An extensive nonblistering first-degree sunburn can make the victim nauseated and weak, with low-grade fever and chills. This victim should be encouraged to drink enough balanced electrolyte liquids to avoid dehydration. Since the skin is the major thermoregulatory organ of the body, a diffuse sunburn will make the victim more prone to hypothermia upon exposure to cold. This is obviously problematic for a diver. It will also be painful to don and doff dive equipment, as the straps rub across sensitive burned skin.
Topical steroid creams may be used if blisters are not present. Topical steroid preparations should not be applied to blistered skin, because wound healing may be delayed and infection potentiated. On the other hand, aloe vera lotion or gel may be soothing and promote healing. Vitamin E is an antioxidant that, when mixed with aloe vera, may soothe the skin. However, this hasn't been proven to promote healing any better than aloe vera alone.
With severe sunburn in which blistering is present, the victim has by definition suffered second-degree burns. Gently clean the burned areas and cover with sterile dressings over antiseptic ointment or cream.
Sunscreens absorb light of a particular wavelength, act as barriers or reflect light. A traveler should choose sunscreens based on the estimated exposure and on his own propensity to tan or burn. Remember that there is no such thing as a safe tan, as sun exposure is directly linked to skin cancer. In addition, long-term exposure to ultraviolet radiation from sunlight causes premature skin aging and loss of skin tone. "Photoaging" refers to these effects, and is characterized by increased wrinkles, loose skin, brown spots, a leathery appearance and uneven pigmentation.
Para-aminobenzoic acid (PABA) derivatives, which are water-soluble, are sunscreens that absorb UVB (not UVA) and accumulate in the skin with repeated application. The most commonly used PABA derivative is padimate O (octyl dimethyl PABA). The most effective method of application is to moisturize the skin (shower or bathe) and then apply the sunscreen. For maximum effect, this should be done at least 15 to 30 minutes prior to exposure, and the skin should be kept dry for at least two hours after sunscreen application.
When PABA itself is used, a recommended preparation is 5 to 10 percent PABA in 50 to 70 percent alcohol. However, PABA is now used infrequently because its absorption peak of UVB at 296 nm is too far from 307 nm, where UVB exerts its greatest effect. Furthermore, it causes skin irritation, a stinging sensation, and can stain cotton and synthetic fabrics. The PABA derivatives are less problematic.
Benzophenones are sunscreens that are more effective against UVA. These should be used in 6- to 10-percent concentration. Because they are not well-absorbed by the skin, they require frequent reapplication. PhotoplexTM is a broad-spectrum sunscreen lotion that contains a PABA-ester combined with a potent UVA absorber, Parsol 1789. This is an excellent sunscreen for sensitive people, particularly those at risk for drug-induced photosensitivity.
Sunscreens come in different concentrations. A higher sun protection factor (SPF) number (range 2 to 50) indicates a greater degree of protection against UVB. The SPF number assumes a liberal (approximately 1.25 ounces per adult) application of the sunscreen. In general, a sunscreen with an SPF number of 8 or less will allow tanning, probably by UVA exposure. People with sensitive or unconditioned skin should use a sunscreen with an SPF number of 10 or greater. Fair-skinned people who never tan or tan poorly (types I, II or III) should always use a sunscreen with an SPF number of 15 or greater.
"Substantivity" refers to the ability of a sunscreen to resist water wash-off. Good waterproof choices include VaselineTM 15, PreSunTM 29, SundownTM 30, BullfrogTM 36, Sawyer Products Bonding BaseTM 45, SolbarTM 50 and AloegaterTM 40. Layering sunscreens doesn't work well, as the last layer applied usually washes off.
Waterproof sunscreens applied to cool, dry skin should be used at least 10 minutes prior to water exposure for proper absorption. They should be reapplied liberally after swimming or heavy perspiration.
Some authorities recommend using a sunscreen of at least SPF 29, with the rationale that most people underapply or improperly apply them. Bald-headed men should protect their domes. All children should be adequately protected. However, avoid PABA-containing products in children less than 6 months old. Persons sensitive to PABA may use Piz-Buin,TM Ti-Screen,TM Sawyer Products Bonding BaseTM 45, Uval and Solbar products. Eating PABA does not protect the skin.
For total protection against ultraviolet and visible light, a sunblock can be prepared from various mixtures of titanium dioxide, red petrolatum, talc, zinc oxide, kaolin, red ferric oxide (calamine) and icthammol. These preparations or similar commercial products ("glacier cream") are used for lip and nose protection. Micronized titanium dioxide can be prepared in an invisible preparation (e.g., TiScreen NaturalTM 16 and Neutrogena Chemical FreeTM 17) that does not cause skin irritation. Sunblocks that prevent infrared transmission may help prevent flares of fever blisters caused by the herpes virus.
Substances that are ineffective as sunscreens and that may increase the propensity to burn include baby oil, cocoa butter and mineral oil.
Many effective sunscreens, particularly those advertised to stay on in the water, are extremely irritating to the eyes, so take care when applying these to the forehead and nose. Near the eyes, avoid sunscreens with an alcohol or propylene glycol base. Instead, use a sunscreen cream.
There are also newer sunscreen/ insect repellent combinations, such as Coppertone Bug & SunTM and Banana Boat Bite Block.TM Bug GuardTM contains Skin-So-SoftTM (mostly mineral oil) in combination with citronella, enhanced by a sunscreen.
A new line of medical clothing, Solumbra® by Sun Precautions, is advertised to be "soft, lightweight and comfortable," and offers 30+ SPF protection. The phone number for the company is (800) 882-7860. Frogskin, Inc., (800) 845-9531, also manufactures high-SPF protective clothing. Sunday Afternoons, (888) 874-2642, manufactures comfortable broad-brimmed hats with neck shields advertised to provide a 97-percent UV block.
Melanoma is a type of skin cancer that can be caused by UVB light exposure. Regular use of a sunscreen with sun protective factor (SPF) of at least 15 during the first 18 years of life may reduce the lifetime risk of developing melanoma by more than 75 percent. Persons with light skin and a tendency to burn rather than tan are at increased risk for the development of melanoma.
If you spend a great deal of time outdoors, it's important to recognize the features of skin cancer. (See the sidebar "Skin Cancer Self-Exam.") You should regularly inspect existing moles, birthmarks and other skin lesions. Since melanoma is often found on a person's back or other area that cannot be easily inspected, it is wise see a dermatologist for a proper evaluation.
Exposure to UVR can lead to a "sunburn" of the cornea (clear surface of the eye). This most often is a problem for a diver if he or she stares out over open water for a prolonged period of time. Skiers and mountaineers call this phenomenon "snowblindness." The cornea absorbs UVR below 300 nm, which includes a fair portion of UVB. Radiation of wavelengths longer than 300 nm is transmitted to the lens of the eye and over time can cause a cataract.
High exposure to UVB can cause a corneal burn within one hour, although symptoms may not become apparent for six to 12 hours. Symptoms include excessive tearing, pain, redness, swollen eyelids, pain when looking at the light, headache, a gritty sensation in the eyes and decreased (hazy) vision. Similar symptoms occur when the surface of the eye is physically scratched.
To avoid corneal damage from the sun, wear protective eyeglasses or sunglasses. The lenses should block 99.8 percent of UVB light. If they are advertised for mountaineering or specifically for ultraviolet protection, they also block out considerable UVA light.
Sunglasses should be equipped with side protectors and, if necessary, optional nose guards. Frames should be prepared with wraparound temples and retaining straps or lanyards. Polycarbonate lenses, which are lightweight, scratch-resistant and shatterproof, can be manufactured to absorb 99 percent of ultraviolet light. In general, amber, yellow, orange, brown or rose lenses filter out blue light and increase the perception of contrast. Green and gray lenses soften glare and transmit a spectrum that does not increase contrast. Glass ambermatic or photochromic lenses (darker in bright sunlight), which contain millions of silver halide crystals, darken when exposed to ultraviolet light close to the visible spectrum.
So enjoy the warmth, but don't "worship" the sun. Respecting the power of solar radiation and keeping yourself well-protected is the best way to maintain a good complexion, sharp vision and a healthy, uninterrupted dive trip.