There are three main types of hyperthermia or heat stress: 1) heat cramps, 2) heat exhaustion, and 3) heat stroke. A fourth type, prickly heat rash, is an annoying but less disabling form of heat stress. Heat cramps and heat exhaustion result from dehydration and salt depletion as the body sweats to lower its internal temperature. Heat stroke occurs when the body core temperature exceeds 41°C (105°F) because its cooling mechanisms have broken down. This condition can cause death. Heat stroke requires immediate medical attention. You can avoid almost all cases of hyperthermia by taking preventative measures.

These painful spasms usually occur in your arm and leg muscles. They can be disabling, but they are preventable if you pay attention to replacing the salt and water lost through sweating. Heat cramps can be treated by gently stretching the muscle, applying ice, and by rehydration.

Heat exhaustion occurs when your body cannot get rid of the heat it generates from metabolism and exercise. If you do not replace the fluids lost through sweating, you may develop heat exhaustion. Although a person suffering from heat exhaustion can continue to produce sweat, the production is not great enough to cool the body satisfactorily. While there is no significant rise in the core body temperature of a victim of heat exhaustion, the condition can rapidly develop into heat stroke. The symptoms for heat exhaustion are the same as for shock.

SYMPTOMS of Heat Exhaustion:

  • Cool clammy skin
  • Weakness or fatigue
  • Headache
  • Nausea, vomiting
  • Muscle cramps
  • Dizziness
  • Confusion

Remove the victim to a cool area. Cool the victim if necessary, and replace the water and salt lost by dehydration. Have the victim lie down with feet elevated. Although a victim of heat exhaustion may feel better almost immediately and wish to return to work, 24 hours of rest is needed for adequate rehydration to occur.

Heat stroke is a life-threatening condition demanding immediate medical attention. As the body core temperature approaches 41°C or 105°F, the victim can no longer produce sweat. The skin usually becomes hot and dry (classic heat stroke). Be aware, however, that the skin may remain relatively cool and clammy with exertional heat stroke. If the core body temperature continues to rise, the victim will die. Exertional heat stroke more commonly occurs to field workers than classic heat stroke. Provide interim treatment and transport victims of heat stroke to a medical treatment facility as soon as possible as complications frequently develop.

SYMPTOMS of Exertional Heat Stroke:

  • Pale, cool damp skin or hot, dry, red skin
  • Irrational, hostile behaviour
  • Rapidly rising core temperature
  • Headache, dizziness
  • Nausea and vomiting
  • Collapse

SYMPTOMS of Classic Heat Stroke:

  • Hot dry skin
  • Rapidly rising core temperature
  • Rapid pulse
  • Headache
  • Nausea and vomiting
  • Delirium
  • Convulsions
  • Collapse and coma

INTERIM TREATMENT – prior to evacuation to a medical center:

  1. Get the victim out of the sun into the coolest possible location.
  2. Loosen tight clothing and elevate the feet.
  3. Cool the victim as quickly as possible, paying particular attention to the head, armpits, and groin. Drape the victim with lukewarm wet sheets or towels to conduct heat away from the body.
  4. Fan the body using electric or hand-held fans. Try to place the victim on a screen so they can be cooled both from above and below. The aim is maximize evaporation from the body to cool the core body temperature – without chilling the victim.


  • An efficient way to cool an overheated field worker is to douse the victim with lukewarm water or cover with wet clothing. Place the victim in a vehicle with the windows down so that he or she is exposed to the moving air. Drive back to a medical treatment facility or rest area, as needed.
  • Use water, wet blankets, or wet clothing to cool the skin of the victim.
  • Use water with a temperature that is warm to the touch but cooler than skin temperature. This temperature produces the best cooling effect by evaporation and conduction. Water that is too cold will effectively shut down the blood supply to the skin. It can also induce shivering as the body works to warm up that local area.


This skin condition is common in the tropics. It is aggravated by high humidity. Tiny droplets of sweat become trapped under the outer layer of skin. These droplets appear as an irritating, blister-like red rash. Frequent showering helps prevent its development. Sometimes a drying lotion and a mild talcum powder help, but ointments and creams will clog up the outlets of your sweat glands even further.

The sun produces ultraviolet radiation that can cause serious burns to your eyes and skin. Both direct and reflected radiation cause burning, and the best way to avoid sunburn is to avoid exposure as much as possible. You can do this by wearing sunglasses with polarizing lenses and by using sunscreen on your exposed skin. Various products are available that contain agents to block out UV radiation. Skin damage from repeated episodes of sunburn can lead to skin cancer, including melanoma. Pay special attention to your hands; field workers frequently develop skin cancers on their hands due to prolonged exposure to the sun.

Factors influencing UV radiation exposure:

  • Altitude: An increase of 300 meters (1,000 feet) in elevation causes an increase in UV radiation of 4%. High altitude results in high UV exposure year round.
  • Latitude: The closer one is to the equator, the more intense the UV radiation.
  • Time of day: UV radiation causes most damage between 10 a.m. and 3 p.m. when the sun is highest in the sky.
  • Season of the year: Except near the equator, the UV radiation is more intense during summer months when the sun is closer to Earth.
  • Wind: Wind masks the effect of UV radiation.
  • Filters: Sunglasses fitted with polarizing lenses will cut down UV radiation exposure to your eyes.
  • Ozone depletion of upper atmosphere: Some areas on Earth are now less protected from UV radiation due to ozone depletion (Arctic, Antarctic, southern South America, Australia).
  • Environment: Depending upon your surroundings, varying amounts of UV radiation will be reflected. For example:

Vegetation reflects only 2.5%.
Sand reflects 20%.
Glaciers and snowfields reflect 85%.
Water can reflect almost 100% if the sun is overhead.


  • Keep the sunburned area covered loosely to stop exposure to more sun.
  • Cold compresses help; creams or lotions may help, but do not apply them to blisters.


  • Wear a broad brimmed hat, shirt, long pants, sunglasses, and sunscreen when appropriate. Shorts expose your legs to sunburn.
  • Wear a broad spectrum, water-resistant sunscreen with a SPF of at least 15 (on your face use an SPF of at least 30). You need this amount of protection – no matter what your race. For full effect, apply sunscreen carefully and thoroughly to exposed skin, especially on your hands, at least 15 minutes before you go out.
  • Sunscreen agents: A sunscreen’s effectiveness is measured by a number called a sun protection factor (SPF). The higher the number, the longer you are protected from burning. That is, if the SPF is 10, then you are protected 10 times longer than if you use no sunscreen. This effectiveness is reduced if you are sweating or swimming. For continuous protection, you must apply sunscreen frequently to exposed skin, especially if swimming or sweating.
  • Taking certain medications often increases a person’s sensitivity to UV radiation. These include tetracyclines, sulphonamides, and oral anti-diabetics.