Many areas of the country will experience extreme temperatures this summer, and sadly the news has been full of stories about the lives lost due to heat stroke. While newscasters warn to stay out of the heat, many workers do not have that option. Keeping workers cool and well-hydrated are the best ways to protect them when working in hot environments.

Risk factors for heat illness

Workers should be made aware of the many risk factors that may affect their heat tolerance. Risk factors that may influence heat illness include high air temperatures and humidity, direct sun exposure, indoor radiant heat sources (ovens, hot manufacturing processes, etc.), limited air movement, physical exertion, not drinking enough fluids (dehydration), personal protective equipment or clothing, certain medications, physical condition, lack of recent exposure (not acclimatized), and advanced age (65+). Workers should discuss their individual risk factors with their healthcare provider.

Staying hydrated

The average person has 2.6 million sweat glands. These glands are activated when a portion of the brain determines that the body needs to be cooled down. Sweat evaporates off our skin which allows for heat loss and cooling. However, when we sweat, we also lose water and electrolytes (i.e., “salts” such as sodium, chloride, potassium). Drinking enough water and having enough electrolytes is necessary for our bodies to function properly. This is why it is so important to stay hydrated; a dehydrated person is likely to start having symptoms of heat illness.

NIOSH (National Institute for Occupational Safety & Health) recommends that for moderate activity in moderate conditions, each worker should drink 1 cup of water every 15 to 20 minutes. Workers should be reminded to drink water frequently before becoming thirsty in order to maintain good hydration. While some workers may prefer the taste of sports drinks, often these types of drinks are not necessary for electrolyte replacement. Workers that eat regular meals and salt-containing snacks will usually be able to replace electrolytes lost during sweating.

In addition to providing plenty of water in convenient locations close to the work site, employers can provide urine color charts near toilet facilities. These charts show the urine colors of a hydrated person compared to a dehydrated person. The darker the urine, the more likely your body is dehydrated.

Keeping cool

Even when the body is at rest, we are internally producing heat through metabolism (breaking down the food we eat into energy). However, during physical exertion, working muscle produces heat at a much higher, faster rate. This increased heat production can result in an increase in body temperature, which above a certain temperature, can be difficult to control. Therefore, it is important to develop ways to cool down the body to help maintain core temperature and reduce the negative effects of thermal stress.

Workers should be allowed to take regular rest breaks. Breaks should be held in a shaded or air conditioned area. Employers and supervisors should be monitoring weather reports daily, and if possible, jobs with high heat exposure should be rescheduled to cooler times of the day. The use of reflective clothing, water-dampened cotton clothing (although this may not work when the humidity is very high), and cooling vests with pockets for cold packs may also be beneficial for keeping workers not only cooler for longer periods of time, but also safer.

Myths about heat stress

There are many misconceptions about heat stress, heat illnesses, and what a person should do when they are required to work hard in a hot environment. The following examples are a few of the myths and common misunderstandings about heat stress and heat illnesses.

MYTH: The difference between heat exhaustion and heat stroke is there is no sweating with heat stroke.

Exertional heat stroke victims may continue to produce sweat [Dept. of the Army and Air Force Technical Bulletin 2003; Armstrong et al. 2007; Navy Environmental Health center 2007]. If a worker is experiencing symptoms of heat stroke (confusion, loss of consciousness, seizures, high body temperature), whether they are sweating or not, it is a life-threatening emergency! Call 911 and try to cool the worker down.

MYTH: Taking a break in the air conditioning will ruin your acclimatization.

Acclimatization can usually be maintained for a few days of non-heat exposure, so taking a break in the air conditioning will not reduce a worker’s level of acclimatization. And it is a very effective way for workers to cool down in a fairly short period of time.

MYTH: Acclimatization will protect you during a heat wave.

Acclimatization occurs when a person is exposed to extreme environmental conditions over a 7-10 day period. However, during heat waves air temperatures rise above normal quickly, and workers will not be able to immediately acclimatize to the new, hotter temperatures. During heat waves, workers will need more breaks and rescheduling some of the harder and hotter job tasks may be warranted.

MYTH: Salt tablets are a great way to restore electrolytes lost during sweating.

Salt tablets should never be used unless a worker is instructed to do so by their doctor. Most people are able to restore electrolytes through normal meals and snacks. Workers should drink plenty of water with their meals and snacks, not only to stay hydrated but also to aid digestion. Moreover, ingestion of too much salt may cause nausea and vomiting which can worsen the level dehydration already present.

MYTH: My medications/health condition will not affect my ability to work safely in the heat.

A worker’s health and medication usage may affect how their body handles high temperatures and heavy physical exertion. Some health problems that may put a worker at a greater heat illness risk include: obesity, diabetes, cardiovascular disease, and even common colds and the flu—especially if the illness is accompanied by a fever and vomiting. Certain medications may affect the body’s ability to cool down or may cause the body to heat up more quickly. Examples of medications that increase risk are diuretics, antihypertensives, and anticholinergics. Workers with health conditions or who are taking medications should discuss with their physicians about how they may be at additional risk if working in a hot environment.

NIOSH is working with the Occupational Safety and Health Administration (OSHA) and other partners to provide heat illness information for employers and workers.


  1. Armstrong LE, Casa DJ, Millard-Stafford M, Moran DS, Pyne SW, Roberts WO [2007]. American College of Sports Medicine position stand. Exertional heat illness during training and competition. Med Sci Sports Exerc 39(3): 556-572.
  2. Navy Environmental Health Center (2007). Prevention and Treatment of Heat and Cold Stress Injuries. Vol Technical Manual NEHC-TM-OEM 6260.6A. Portsmouth, Virginia. Available at:
  3. Department of the Army and Air Force Technical Bulletin (2003). Heat Stress Control and Heat Casualty Management. Available at: