Heat and cold can be directly or indirectly responsible for some illnesses and can contribute to exacerbations of pre-existing medical problems. In addition to the actual temperature, environmental factors such as humidity and wind velocity can contribute to loss of ability to adequately regulate one’s body temperature.

Heat

People have heat-related illness when their bodies are unable to compensate and properly cool themselves. In such cases, the body temperature rises rapidly. Very high body temperatures may damage the brain or other vital organs. Sweating is the normal physiologic mechanism for the dissipation of excess body heat. When the humidity is high, sweat will not evaporate as quickly, preventing the body from releasing heat rapidly. Those at greatest risk for heat-related illness include infants and young children, people over 65 years of age, people who are overweight, people with existing cardiac disease, and people who are taking certain medications. However, healthy individuals of any age can also be affected if they participate in strenuous physical activities while traveling in hot conditions.

HEAT EXHAUSTION

Heat exhaustion is a milder form of heat-related illness that can develop after several days of exposure to high temperatures and inadequate or unbalanced replacement of fluids. Symptoms include headache, fatigue, nausea, a rapid pulse, and heavy sweating.

HEATSTROKE

Heatstroke is the most serious heat-related illness (1). It occurs when the ability to control body temperature is overcome: core temperature rises, and the ability to sweat and therefore cool down is lost. Body temperatures can rise to 106° F or higher within 10-15 minutes. Heatstroke can cause death or permanent disability if emergency treatment is not provided. Symptoms include an extremely high body temperature (above 103° F); red, hot, and dry skin (no sweating); a rapid, strong pulse; headache; dizziness; and nausea.

PREVENTION

Travelers should be made aware that acclimatization may take days. Travelers in hot climates should increase their fluid intake, particularly during vigorous exercise (2). To avoid dehydration, travelers should be advised not to wait until they are thirsty to drink. During heavy exertion in a hot environment, the goal should be to drink two to four glasses (16-32 ounces) of cool fluids each hour; liquids that contain alcohol or large amounts of sugar should be avoided, as they can exacerbate dehydration. A sports beverage can replace the salt and minerals lost in sweat, although in most circumstances plain water will suffice.

Travelers in very hot climates should consider limiting activities to morning and evening hours (when it is often cooler) and resting as often as needed. Protection can be increased by wearing a hat and by making sure to use sunscreen, even on cloudy days. Although fans may increase personal comfort, if tempera-tures are extremely high the movement of hot air may actually increase health risk (3). During the warmer hours, it is preferable to seek activities in air-conditioned facilities (4).

TREATMENT

Persons with symptoms suggestive of heat exhaustion should rest, drink cool nonalcoholic beverages, and try to lower their body temperature with a cool shower, bath, or swim. If symptoms do not start to resolve within an hour or if they progress to those of heatstroke, attempts to lower the body temperature should be continued and medical attention should be sought immediately.

Cold

Excessive cold affects persons who are inadequately dressed or who remain outside for extended periods of time in cold climates. Cold particularly affects two groups of people: the elderly, because they have slower metabolisms, and the young, because infants and children lose body heat more easily than do adults and are unable to generate sufficient body heat by shivering.

HYPOTHERMIA

Hypothermia usually occurs at very cold temperatures but can occur at cool temperatures if a person becomes chilled from rain, sweat, or submersion in cold water, or if exposure occurs during cold windy conditions. The warning signs of hypothermia include shivering, confusion, memory loss, drowsiness, exhaustion, fumbling hands, and slurred speech. If the body temperature of someone with these signs is <95° F, medical attention should be sought immediately.

FROSTBITE

Frostbite occurs under very cold conditions when tissues actually freeze, meaning that ice crystals form within the cells, causing them to rupture (5). Frostbitten skin appears white or grayish-yellow and becomes unusually firm or waxy and numb. Frostbite most often affects the nose, ears, cheeks, chin, fingers, and toes.

PREVENTION

To prevent hypothermia and frostbite, travelers should dress warmly in layers with a hat, scarf, mittens, sweater, and coat. (6) The outer layer of clothing should be tightly woven and preferably wind and water resistant, to reduce body-heat loss caused by wind. Wool, silk, or polypropylene inner layers of clothing will retain more body heat than cotton. Excess perspiration will increase heat loss, so extra layers of clothing can be removed if they become unnecessary. Travelers should also wear waterproof shoes to avoid wet, cold feet. In cold conditions, drinking warm beverages and avoiding alcohol will also help maintain an appropriate body temperature.

TREATMENT

First aid for these cold-related conditions includes getting the person warm (7). Persons with symptoms suggestive of hypothermia or frostbite should seek emergency medical attention.

References

1. Bouchama A, Knochel JP. Heat stroke. N Engl J Med. 2002;346:1978-88.
2. CDC. Heat-related mortality-Arizona, 1993-2002, and United States 1979-2002. MMWR Morbid Mortal Wkly Rep. 2005;54:628.
3. Semenza J, Rubin C, Falter K, Selanikio J, Flanders W, Howe H, et al. Heat-related deaths during the July 1995 heat wave in Chicago. N Engl J Med.1996;335:84-90.
4. Naughton MP, Henderson A, Mirabelli MC, Kaiser R, Wilhelm JL, Kieszak SM, et al. Heat-related mortality during the 1999 heat wave in Chicago. Am J Prev Med. 2002;22:221-7.
5. Murphy JV, Banwell PE, Roberts AH, McGrouther DA. Frostbite: pathogenesis and treatment. J Trauma. 2000;48:171-8.
6. CDC. Hypothermia-related deaths-United States, 1999-2002 and 2005. MMWR Morbid Mortal Wkly Rep. 2006; 55: 282-4.
7. Biem J, Koehncke N, Classen D, Dosman J. Out of the cold: management of hypothermia and frostbite. CMAJ. 2003;168:305-11.

CAROL RUBIN