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Chapter 3 Environmental Hazards & Other Noninfectious Health Risks

Sun Exposure

Karolyn A. Wanat, Scott A. Norton

When international travelers engage in outdoor activities, they may be exposed to more ultraviolet (UV) radiation than usual, particularly in sunny locations or at high elevations. Even winter activities, such as snow skiing, can result in significant UV exposure. Short bursts of high-intensity UV radiation (such as the occasional beach vacation) as well as frequent, prolonged, cumulative UV exposure can cause acute effects, such as sunburn and phototoxic medication reactions, and delayed effects, such as sun damage, premature aging, and skin cancers.

RISK FACTORS

Time of year, time of day, and location of exposure influence the amount of UV exposure a traveler receives. Most UV light reaches the earth’s surface during summer months. UVB, which is more carcinogenic than UVA, is most intense between the hours of 10 am and 4 pm, at higher elevations, and in locations closer to the equator. Water, sand, and snow reflect UV light and therefore increase UVB exposure.

People with certain medical conditions are at increased risk for adverse effects of UV exposure. Solid-organ transplant recipients, for example, are at much higher risk for UVB-induced skin cancers. People with autoimmune connective tissue diseases (such as systemic lupus erythematosus) exhibit heightened photosensitivity. These patients should receive counseling about how best to protect themselves during hours of maximal exposure. Moreover, many medications, including several prescribed specifically for travelers, can lead to photosensitivity reactions:

  • Acetazolamide
  • Antibiotics, including doxycycline (and other tetracyclines to a lesser degree), fluoroquinolones, sulfonamides
  • Nonsteroidal anti-inflammatory drugs (NSAIDs), especially naproxen, piroxicam, ketoprofen
  • Other common medications, such as furosemide, thiazide diuretics, methotrexate, and sulfonylureas

CONSEQUENCES

Sunburn

Sunburn is a common and self-limited condition. Clinical features vary from mild pink to painful red skin with edema and blistering on exposed surfaces. Systemic symptoms may include headache, fever, nausea, vomiting, and myalgia. Management involves symptomatic pain relief. People rarely notice they are developing a sunburn as the burn occurs. Cool compresses and bland topical emollients (such as petrolatum or zinc oxide) may be applied. Refrigerating topical emollients before application can provide added relief. Aloe vera is used commonly as a sunburn remedy, but studies are equivocal regarding its benefit.

Intact blisters should not be ruptured intentionally. Topical corticosteroids (such as hydrocortisone 1% cream or ointment) or diclofenac gel may decrease pain and inflammation. Patients typically derive benefit from oral pain relievers such as acetaminophen, aspirin, or other NSAIDs. Systemic steroids do not improve symptoms or hasten recovery.

Severe or extensive sunburns may cause fever, headache, vomiting, or dehydration; treatment includes avoidance of further sun exposure, rest in a cool setting, fluid replacement, and NSAIDs. For severe, blistering cases, it may be necessary to hospitalize the patient for fluid replacement (oral or intravenous) and pain control, similar to burn victims. It is important to maintain clean skin with gentle cleansing and treatment with emollients.

Sun Damage and Skin Cancer

High-intensity or chronic exposure to UV radiation causes permanent loss of skin elasticity, wrinkling, and solar lentigines (brown macules with irregular borders), especially in fair-skinned people. Preventing sunburn and sun overexposure is the best way to avoid these changes.

Development of skin cancers (basal and squamous cell carcinomas [BCCs and SCCs]) is linked closely to UV exposure. BCCs typically appear as pearly or bleeding papules or ulcers or ulcerated papules, often on sun-exposed areas. These tumors rarely metastasize and can be cured with excision or other methods.

SCCs present on sun-exposed areas as scaling or bleeding papules or plaques. SCCs are 10 times more likely to metastasize than are BCCs. Solid-organ transplant patients receiving immunosuppressive therapy and patients with chronic lymphocytic leukemia are at increased risk of SCC.

Only approximately 5% of skin cancers are melanomas, although the incidence is increasing in most populations. In addition to fair skin and genetics, having had blistering sunburns before the age of 18 also is a risk factor. Melanomas are associated with the highest rates of morbidity and mortality, but early detection and treatment ensure nearly complete recovery. Melanomas can have a variety of clinical presentations, the most common of which is an irregularly bordered macule or papule. Depending on the tumor stage, surgical excision with adjuvant therapy may be required.

Intermittent intense sun exposure and blistering sunburns are associated with the development of BCC and cutaneous melanoma, whereas chronic and cumulative sun exposure is more associated with SCC. This explains the observation that people with infrequent vacations spent sunbathing in tropical areas are at greatly increased risk for melanoma.

Other Photosensitive Disorders

Increased sun exposure can exacerbate existing skin conditions and can unmask photosensitive disorders, such as polymorphous light eruption, solar urticaria, porphyrias, and autoimmune connective tissue diseases such as dermatomyositis or systemic lupus erythematosus. If sun exposure causes prolonged or severe symptoms (such as swelling, pruritus, arthralgias, fever), medical evaluation is warranted.

Phytophotodermatitis is a noninfectious condition that results from interaction of natural psoralens, most commonly found in the juice of tropical limes, and UVA radiation from the sun. The result is an exaggerated sunburn that creates a painful line of blisters, followed by asymptomatic hyperpigmented lines that may take weeks or months to resolve.

Photo-onycholysis, a separation or lifting of the nail plate from the nail bed, is described in people taking doxycycline after a day of intense sun exposure. The most common setting is someone taking doxycycline for malaria prophylaxis during a trip to a tropical location.

PREVENTION

Travel preparation should include planning to prevent sun overexposure. Awareness that UVB radiation is highest during midday and that UV exposure still occurs in cooler weather and on overcast days is necessary to guide general safe sun behaviors. UV exposure increases with travel to lower latitudes (closer to the equator) or to higher elevations.

Sunscreens

Sunscreens are topical preparations that can reflect or absorb UV radiation. They may contain organic substances that filter (absorb or capture) UV radiation, inorganic products that reflect UV radiation, or both. Inorganic agents contain micropulverized metallic nanoparticles of zinc oxide or titanium dioxide, which both reflect and absorb UV radiation.

The most effective sunscreens are “broad spectrum,” combining agents capable of reflecting and filtering both UVA and UVB radiation. The US Food and Drug Administration’s current labeling guidelines, adopted in 2010, indicate that broad-spectrum sunscreen products with a sun protection factor (SPF) ≥15 may state, “If used as directed with other sun-protection measures, [this product] decreases the risk of skin cancer and early skin aging caused by the sun.” The same labeling guidelines do not permit manufacturers to claim that products are waterproof or sweatproof; sunscreens may be labeled “water resistant” (up to either 40 or 80 minutes).

Recommendations for sunscreen use include:

  • Before going outside, apply broad-spectrum sunscreen (SPF ≥15) to protect skin from both UVA and UVB, even on cloudy or cool days. Some professional organizations, such as the American Academy of Dermatology, recommend using sunscreens with an SPF ≥30. Apply sunscreen liberally to create a thin film on all exposed body surface areas, obtaining assistance to apply to difficult-to-reach areas.
  • Reapply every 2–3 hours and promptly after sweating or being in the water, as sunscreens are neither waterproof nor sweatproof.
  • Make sure that the sunscreen is not past its expiration date.
  • When also using insect repellent, apply sunscreen first, let it dry, then apply repellent. Very limited data suggest that DEET-containing insect repellents can attenuate the UVB protection provided by sunscreen, by as much as one-third of the reported SPF. Sunscreens may increase the absorption of DEET through the skin.
  • Avoid products that contain both sunscreen and insect repellent.

Inorganic sunscreens cover a broad spectrum of UV radiation and are associated with a reduced risk of allergic or irritant contact dermatitis. Although they may leave a thin, white film on the skin, they are cosmetically more acceptable than the thick, opaque pastes associated with older products. By contrast, organic sunscreens are easier to apply and less likely to leave a visible film but may trigger a sensitivity or allergic reaction. If this happens, using an inorganic sunscreen may be an alternative.

Travelers may also opt (or be required, in some locations) to use inorganic sunscreens due to the reported adverse environmental effects of the organic sunscreens: oxybenzone, 4-methylbenzylidene camphor, octocrylene, and octinoxate. In 2018, for example, Hawaii passed a law banning sunscreens containing octinoxate and oxybenzone in response to evidence of their toxicity to coral marine life.

Babies <6 months of age should have only minimal exposure to direct sunlight. Protect infants by using covered strollers, umbrellas/parasols, and hats, rather than by applying sunscreen.

Protective Clothing

Sun-protective garments (for example, pants, long-sleeved shirts, and hats) can protect against UV radiation. Efficacy depends on the fabric. A cotton t-shirt (SPF ≤15) affords even less protection when the shirt is wet. Thicker fabrics with tighter weaves, such as denim, offer high SPF protection. Travelers can treat lighter-weight fabrics (nylon and cotton) with UV-filtering dyes and other products to enhance UV protection.

Other protective measures include hats and sunglasses. Hats with a wide circumferential brim (at least 3 inches in diameter) that shades the face, neck, and ears are ideal. Lightweight kepi-style (“French Foreign Legion”) sunhats, with a flap to cover the neck and ears, are quite effective, especially for children. These protect the skin much more than a baseball cap. Wrap-around sunglasses or those with sun-blocking sidepieces provide the best UV protection.

Sun Avoidance

If possible, avoiding direct sun during peak hours (10 am to 4 pm) will decrease UV exposure. Seeking shade under trees, umbrellas, or other structures will also reduce UV exposure, although UV rays can still reflect off substances such as water, snow, and sand.

BIBLIOGRAPHY

  1. American Cancer Society. Skin cancer. [cited 2018 Mar 17]. Available from: www.cancer.org/cancer/skin-cancer.html.
  2. Diaz JH, Nesbitt Jr. T. Sun exposure behavior and protection: recommendations for travelers. J Travel Med. 2013; 20(2):108–118.
  3. Monteiro AF, Rato M, Martins C. Drug-induced photosensitivity: photoallergic and phototoxic reactions. Clin Dermatol 2016; 34:571.
  4. Skin Cancer Foundations. Sun protection. [cited 2018 Mar 17]. Available from: www.skincancer.org/prevention/sun-protection.
  5. Young AR, Claveau J, Rossi AB. Ultraviolet radiation and the skin: photobiology and sunscreen photoprotection. J Am Acad Dermatol 2017; 76:S100.
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