The dangers presented by hot weather are often overlooked, but last summer, an unusually long and extreme heat wave throughout Europe resulted in thousands of deaths. Travelers need to be aware of the risk of heat-related emergencies. Dehydration in particular is a common travel hazard.

Dehydration occurs when the body loses the water and essential body salts (electrolytes) needed to maintain normal function. Side effects include lack of energy, muscle cramps and back pain. If left untreated, dehydration can lead to exhaustion and heat stroke, which can be fatal.

Most Americans do not drink enough water, and many of us are mildly dehydrated without even knowing it. While the main causes of dehydration include overexposure to the sun and high temperatures, dehydration also strikes people who fly long distances because the air in pressurized airplane cabins is actually drier than the air at most of the world’s deserts. On long-distance flights at high altitudes, the humidity can fall well below 10 percent. Symptoms of in-flight dehydration include thirst, scratchy and/or reddened eyes, dry, itchy skin, constipation and nosebleeds.

There’s no way to avoid some degree of dehydration during long flights, but you can minimize the problem by taking the following steps:

1. Drink plenty of water prior to departure.
2. Carry your own bottle of water to drink throughout the flight.
3. Try to drink a glass of water every hour that you are in the air.
4. Do not drink coffee or alcohol, which deplete body fluids.
5. Use a water spritzer to spray your face periodically.
6. Continue to drink plenty of water after landing.

Heat emergencies fall into three categories of increasing severity: heat cramps, heat exhaustion and heat stroke. Left untreated, heat cramps (caused by loss of salt from heavy sweating) can lead to heat exhaustion (caused by dehydration), which can progress to heat stroke. Heat stroke can cause shock, brain damage, organ failure and death. Common causes of heat-related emergencies include high temperature and humidity, dehydration, prolonged or excessive exercise, excess clothing, alcohol use and certain medications, such as diuretics. Travelers with cardiovascular disease and sweat gland dysfunction can also be prone to heat emergencies.

Early symptoms of heat-related illness include profuse sweating, fatigue, thirst and muscle cramps. As the condition progresses toward heat exhaustion, symptoms include headache, dizziness, weakness and lightheadedness, nausea and vomiting, cool dark skin and dark urine. When heat stroke occurs, symptoms include fever, with a body temperature above 104 degrees, irrational behavior, extreme confusion, dry and hot red skin, rapid shallow breathing and rapid pulse leading to seizures and unconsciousness.

These symptoms warrant immediate medical attention. While waiting for medical personnel to arrive, cool the victim rapidly with whatever is close at hand, be it shade, cold water from a hose, a fan, ice cubes or air conditioning. You should also give fluids to a conscious victim, and turn a vomiting victim on his or her side to avoid aspiration.

Tips for preventing heat-related illness, some of which were covered under dehydration, include:

1. Drink plenty of fluids.
2. Avoid alcoholic and caffeinated beverages.
3. Remain in an air-conditioned environment.
4. Wear lightweight, light-colored, loose-fitting clothing.
5. Limit outdoor activity to morning and evening hours.
6. Limit exercise and/or drink sports beverages to replace salt and minerals lost by sweating.
7. Wear a wide-brimmed hat, sunglasses and sunscreen with an spf of 15 or higher.

For more information about heat stroke and heat-related illness, visit www.cdc.gov/nceh/hsb/extremeheat.