The University of Iowa

Heat Stress

What is Heat Stress?

Heat stress occurs when the body cannot get rid of excess heat. When this happens, the body's core temperature rises and the heart rate increases. As the body continues to store heat, the person begins to lose concentration and has difficulty focusing on a task, may become irritable or sick, and often loses the desire to drink. The next stage is most often fainting and even death if the person is not cooled down.

Factors that contribute to heat stress are high air temperatures, radiant heat sources, high humidity, direct physical contact with hot objects, and strenuous physical activities.

Contact information and areas of expertise can be found on the Contact Us page.

Heat Rash

Also known as prickly heat, is skin irritation caused by sweat that does not evaporate from the skin. Heat rash is the most common problem in hot work environments.


  • Clusters of red bumps on skin
  • Often appears on neck, upper chest, folds of skin

First Aid

  • Try to work in a cooler, less humid environment when possible
  • Keep the affected area dry

Heat Cramps

Are caused by the loss of body salts and fluid during sweating. Low salt levels in muscles cause painful cramps. Tired muscles—those used for performing the work—are usually the ones most affected by cramps. Cramps may occur during or after working hours.


  • Muscle spasms
  • Pain

First Aid

  • Have worker rest in shady, cool area
  • Worker should drink water or other cool beverages
  • Wait a few hours before allowing worker to return to strenuous work
  • Have worker seek medical attention if cramps don't go away

Heat Exhaustion

Is the body's response to loss of water and salt from heavy sweating? 


  • Cool, moist skin
  • Heavy sweating
  • Headache
  • Nausea or vomiting
  • Dizziness
  • Light headedness
  • Weakness
  • Thirst
  • Irritability
  • Fast heart beat

First Aid

  • Have worker sit or lie down in a cool, shady area
  • Give worker plenty of water or other cool beverages to drink
  • Cool worker with cold compresses/ice packs
  • Call 911 if signs or symptoms worsen or do not improve within 60 minutes.
  • Do not return to work that day

Heat Stroke

The most serious form of heat-related illness, happens when the body becomes unable to regulate its core temperature. Sweating stops and the body can no longer rid itself of excess heat.


  • Confusion
  • Fainting
  • Seizures
  • Excessive sweating or red, hot, dry skin
  • Very high body temperature
  • Call 911

While waiting for help:

  • Place worker in shady, cool area
  • Loosen clothing, remove outer clothing
  • Fan air on worker; cold packs in armpits
  • Wet worker with cool water; apply ice packs, cool compresses, or ice if available
  • Provide fluids (preferably water) as soon as possible
  • Stay with worker until help arrives

Prevention of Heat Stress: Supervisors

  • Allow time for employees to adjust to hot jobs when possible. It often takes two to three weeks for an employee to become acclimated to a hot environment.
  • Adjust the work schedule, if possible. Assign heavier work on cooler days or during the cooler part of the day.
  • Reduce the workload. Increase the use of equipment on hot days to reduce physical labor.
  • Establish a schedule for work and rest periods during hot days.
  • Train workers to recognize signs and symptoms of heat stress disorders and be prepared to give first aid if necessary.
  • Choose appropriate employees: Avoid placing "high risk" employees in hot work environments for extended time periods. Realize individual employees vary in their tolerance to heat stress conditions.

Prevention of Heat Stress: Workers

  • Learn to recognize the symptoms of heat stress. Pace the work, taking adequate rest periods (in shade or cooler environment).
  • Use adequate fans for ventilation and cooling, especially when wearing personal protective equipment (PPE).
  • Wear light-colored, loose clothing (unless working around equipment with moving parts).
  • Keep shaded from direct heat where possible (e.g., wear a hat in direct sunshine).
  • Drink plenty of water: in hot environments the body requires more water.

For outside work the heat index can be used to determine the protective measures that need to be taken. The below table from OSHA gives the levels and recommend precautions. Clicking on the risk level will take you to an OSHA page with more information. OSHA and NIOSH have also developed a phone app (OSHA NIOSH Heat Safety Tool) that well show the heat index for your location and give you the recommendations.

Heat Index

Risk Level

Protective Measures

Less than 91°F

Lower (Caution)

Basic heat safety and planning

91°F to 103°F


Implement precautions and heighten awareness

103°F to 115°F


Additional precautions to protect workers

Greater than 115°F

Very High to Extreme

Triggers even more aggressive protective measures