Heat Stress Imposed by PPE Worn in Hot and Humid Environments

Posted on by W. Jon Williams, PhD and Jaclyn Krah Cichowicz, MA


A recent blog discussed prolonged respirator use and the potential physiological burden that could result from the buildup of CO2 within the respirator facepiece. Heat stress is another potential stress factor that healthcare workers (HCWs) who use personal protective equipment (PPE) and their employers should be aware of in order to recognize the signs and be prepared with the knowledge of how to alleviate the burden.

Respirator and Other PPE Use in Warm and Potentially Humid Environments.

HCWs working in warm and humid environments often must wear full coverage PPE, including respirators. When responding to disasters that challenge the resources of the hospital or other healthcare systems, it may become necessary for the HCW to wear the PPE for extended periods of time. Extended wear of PPE increases the wearer’s physiological burden, usually in the form of respiratory stress (addressed in the previous blog) and heat stress. Although most HCWs conduct their work in an indoor setting (hospital, clinic) with environmental controls to keep the workspace comfortable, emergency or pandemic situations may necessitate the rapid construction of field hospitals, which may not have environmental control systems able to create and maintain a comfortable temperature. Under these circumstances, the surrounding environment may achieve levels of heat and humidity great enough to cause discomfort or to become dangerous to the occupants (both HCWs and patients).

The more encapsulating the PPE that workers must wear, the greater their risk of experiencing heat stress and physiological strain.

If the HCW does not have the opportunity to rehydrate by drinking fluids, the sweat loss can contribute to a decrease in blood volume that can lead to low blood pressure and dizziness. In addition to dizziness, core body temperature may increase, which may lead to other symptoms (see list below) (NIOSH, 2016). If the HCW continues to “power through” without being able to rehydrate, then they may not be able to compensate and could easily escalate to heat injury.

Too busy to remember to hydrate? Here’s a tip – when working in a moderately hot setting, set a timer on your phone or smart watch to remind you to drink a cup of water (8 oz.) every 15-20 minutes.

Signs and Symptoms of Heat Stress and Physiological Strain

  • Thirst (although remember that thirst is not a reliable indicator of hydration status)
  • Headache
  • Dark yellow colored urine with a strong odor (compare to a urine color chart for an indication of level of dehydration)
  • Flushed skin
  • Heavy sweating
  • Fatigue (heat exhaustion)
  • Increase in body temperature
  • Dizziness or loss of orientation
  • Decreased cognitive function (decreased situational awareness, poor judgement)
  • Loss of balance, leading to an increased risk of slips, trips, and falls
  • Heat syncope while standing upright (temporary circulatory failure) with symptoms of light-headedness or dizziness.

Taking Control – How you Can Prevent Heat Stress

In order to control the effects of heat stress NIOSH recommends:

  • Limit time in the heat and/or increase recovery time spent in a cool environment.
  • Train supervisors and workers about heat stress that may be found in atypical places such as a healthcare setting while using encapsulating PPE.
  • Implement a buddy system in which workers observe each other for signs and symptoms of physiological heat strain.
  • Provide adequate amounts of cool (15⁰C or 59⁰F) water near the work area and encourage workers to drink frequently. Should employees work for more than 90 minutes continuously in a hot environment accompanied by profuse sweating, then cool (15⁰C or 59⁰F), balanced carbohydrate/electrolyte drinks should be provided in order to prevent hyponatremia or other electrolyte imbalances.
  • Implement a heat alert program whenever the weather service forecasts that a heat wave is likely to occur.

Don’t Self-Contaminate! Donning and Doffing PPE to Prevent Exposure

Workers must remain healthy and focused especially when donning and doffing PPE in order to prevent a possible self-contamination. Any surface of your PPE can become contaminated during use and be a potential source of exposure. Given that fact that heat exposure may affect cognition, it is important to limit heat strain on workers who may have a greater chance of inadvertent self-contamination during the PPE doffing procedure. This is particularly important because there may be an increase in work breaks to limit heat exposure, thereby increasing the number of chances for self-contamination during repeated doffing procedures.

Hand hygiene is another vital step in preventing the spread of any infectious disease. Workers must always perform hand hygiene after removing any PPE, especially gloves as they do not replace the need for completing adequate hand hygiene after use.

To Summarize, Prepare by Being Aware – Recognizing the Signs and Symptoms of Heat Stress

Supervisors should be trained to recognize the signs and symptoms of heat stress. Workers should also be aware of their own health conditions and encouraged to know the limits of when to take a break for personal health and safety. When working in environments with high heat or humidity levels, it is important to take preventative measures such a scheduled breaks (if possible given the circumstances) to visit a rest area and take time away from the immediate work and the discomforts of the PPE (doff the gear). While on break, HCWs should rehydrate either with cool water or balanced carbohydrate/electrolyte “sports” drink, eat some nutritious food, and take enough time to cool off in an air-conditioned area prior to resuming work. Without adequate rest, food, removal from hot environment (or doffing PPE for relief), and hydration, fatigue can set in and increase the possibility of a heat injury or illness.


Warren (Jon) Williams, PhD is a research physiologist in the NIOSH National Personal Protective Technology Laboratory Research Branch

Jaclyn Krah Cichowicz, MA, is a health communications specialist in the NIOSH National Personal Protective Technology Laboratory Research Branch


Other blogs on the effects of prolonged PPE use on healthcare workers include:

The Physiological Burden of Prolonged PPE Use on Healthcare Workers during Long Shifts

Skin Irritation from Prolonged Use of Tight-Fitting Respirators


Additional Resources

Heat Stress Hydration

Hydration Status

NIOSH Heat Stress Topic Page (more resources can be found here)




NIOSH [2016]. NIOSH criteria for a recommended standard: occupational exposure to heat and hot environments. By Jacklitsch B, Williams WJ, Musolin K, Coca A, Kim J-H, Turner N. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication 2016-106.

Posted on by W. Jon Williams, PhD and Jaclyn Krah Cichowicz, MA

3 comments on “Heat Stress Imposed by PPE Worn in Hot and Humid Environments”

Comments listed below are posted by individuals not associated with CDC, unless otherwise stated. These comments do not represent the official views of CDC, and CDC does not guarantee that any information posted by individuals on this site is correct, and disclaims any liability for any loss or damage resulting from reliance on any such information. Read more about our comment policy ».

    I have two questions. A): Can extreme heat conditions allow for the reduction of worn PPE? I am an operations manager for a fuel carrier. At a specific unload site we are required to wear a full accompaniment of PPE as deemed by WorkSafe and the site’s policy. We are also regulated by the C.P.P.I. This particular unload site requires a driver/delivery person to be in direct sunlight during ambient temperatures that exceed 30 degrees Celsius for a period of at least 90 minutes. The actual temperature usually exceeds 35 degrees Celsius. Question B): If the likelihood of heat stress, exhaustion, and all related health concerns are FAR greater than the likelihood of a ‘fire’: Can we reduce the multiple layers of PPE that are worn in case of a fire?

    This is the great conundrum faced by the requirement to wear encapsulating PPE in hot environments. There are only a few approaches but none of them involve the reduction of PPE in the situation you describe. Although the perceived or real risk of a fire is low compared to the risk of a heat related illness or injury due to wearing of PPE in a hot environment, the risk of fire is still present during the offloading procedures and that risk can only be mitigated by the use of PPE. I am not familiar with the details of your operation so this may not be feasible but I would suggest that you have more than one person be involved in the offloading procedure. This allows for a work/rest cycle in which one person is involved in the offloading procedure while the other is resting with full availability of water and, after 30 min, these two workers switch places and the person who was resting is now involved in the offloading process giving the other a break with access to water. This work/rest cycle involving two or more people may limit the heat exposure previously experienced by one individual. This rotation of personnel continues until the offloading procedure is complete. Then all personnel involved can take a rest/water break before they embark on another procedure. If there is an area (inside an air-conditioned building?) where the resting person can safely remove some of the PPE and drink plenty of water, that would be ideal but I am not sure if your situation allows for this. However, I cannot recommend that you reduce the type of PPE use under the circumstances you have described because you would be specifically circumventing the WorkSafe and site policy.

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Page last reviewed: August 14, 2020
Page last updated: August 14, 2020