What’s the difference between heat stress and heat-related illness?

By Safeopedia Staff | Last updated: April 20, 2024
Engineer in a yellow high-visibility jacket, holding a white hardhat in hand, feeling the heat and sweating in an indoor industrial setting.
Source: coffeekai (Envato Elements)

If you ever read anything about heat-related hazards, you’ll encounter a lot of references to heat stress.

That makes sense. It’s the thing workers have to worry about if they do a lot of heavy physical labor, work in a hot environment, or both. It’s also what employers and safety professionals need to control to ensure the safety of their employees.

But you’re probably going to see a lot of references to heat-related illnesses (HRIs) as well.

Those are important, too. Workers who spend a lot of time in the heat or get hot while doing their jobs have to worry about HRIs. And employers and safety professionals have to take steps to keep workers safe from them.

So, you might be wondering if there’s a difference between those two concepts. And if so, what it is.

Well, there is. Even though they’re often talked about in the same breath, heat stress and heat-related illnesses are not actually the same thing. And once we define them, you’ll see what makes them different, and why understanding both of them is important for workplace safety.

Heat Stress Comes First

Put simply, heat stress is the total amount of heat to which the body is exposed.

It’s often discussed in relation to hot weather, but it’s really a combination of different factors:

  • Obviously, there’s environmental heat – the outdoor heat or the heat generated by machinery and other equipment.
  • There’s also the heat produced by the body (metabolic heat), which can be increased by physical exertion.
  • Hydration plays a role as well, since it encourages the production of sweat which has a cooling effect on the body when it evaporates.
  • The clothing or PPE worn over the body makes a difference, too. Breathable fabrics or cooling PPE can reduce the total heat stress on the body, while heavy PPE or thick fabrics can trap heat and worsen heat stress.

Heat stress has been linked to reduced productivity, likely due to how much energy the body has to expend to regulate its internal temperature. If you find yourself slowing down and feeling sluggish on hot days, you’re not alone – it’s a typical response to high heat exposure.

More concerning, though, is the fact that high levels of heat stress can also cause a number of heat-related illnesses.

Then Come the Heat-Related Illnesses

Heat-related illnesses are a cluster of adverse health effects that can occur when the body is subjected to high levels of heat stress. These effects range in widely in severity, from uncomfortable rashes to fatal heat strokes.

There are a number of conditions that fall under the HRI umbrella. But in the context of workplace safety, there are six in particular that get discussed frequently. They are, from the least severe to the most concerning:

  • Heat rash: surface-level skin irritation accompanied by a warm and prickly sensation
  • Heat edema: visibly noticeable swelling or puffiness that results from heat exposure
  • Heat cramps: painful cramping caused by a combination of physical exertion and exposure to heat
  • Heat syncope: dizziness or
    fainting due to heat exposure
  • Heat exhaustion: fatigue, weakness, dizziness, and excessive sweating, which can progress and develop into a heat stroke
  • Heat stroke: cessation of sweating, confusion, loss of consciousness, and, in severe cases, organ failure

Heat rashes and edemas are not really a safety issue, though taking steps to avoid them is advisable. Not only are they unpleasant, but the discomfort can be distracting which can increase the likelihood of inattention, loss of concentration, and small but potentially harmful mistakes.

Heat cramps and heat syncope are a bit more serious. While not severe conditions on their own, they can put workers at serious risk when they happen on the jobsite. The sudden sharp pain of a muscle cramp can cause a worker to drop a heavy object or lose their footing. And a heat-induced fainting spell becomes a major cause for concern for anyone working on a scaffolding or with heavy machinery.

But the reason heat stress gets as much attention as it does is heat stroke, along with the heat exhaustion that leads up to it. It’s a level of overheating that essentially shuts down the body’s normal functioning. It can cause dysfunction in the organs, which can be permanently disabling. If not treated in time, it can lead to multiple organ failure, which is a literal death sentence.

Heat Stress vs. Heat-Related Illnesses

So, now you know the difference between the heat stress and heat-related illnesses.

And you’ll see that the term “heat stress” is often used a bit loosely. People sometimes use it to describe what are really heat-related illnesses, like saying that a person hit with heat exhaustion is “suffering from heat stress.”

That’s not quite right, though.

For one thing, heat stress itself isn’t always a problem. It might sound bad, it’s only hazardous when the total heat stress on a person’s body is high enough to cause them to overheat.

Heat-related illnesses, on the other hand, are always an issue. Sure, some are relatively minor – a heat rash won’t land you in the emergency room and a heat edema is essentially harmless. But there’s no such thing as a good level of heat-related illness – unless it’s none.

But the core difference between these two concepts is simply that heat stress is the cause of the body overheating, while heat-related illnesses are the unfortunate outcomes of that overheating.

Or to put it another way: heat stress is the hazard you have to worry about, and heat-related illnesses are why you have to worry about it.

Don’t be surprised if you keep seeing these terms used a bit loosely, though. Because when it comes to workplace health and safety, managing heat stress and preventing heat-related illnesses are two sides of the same coin. Both require engineering controls and PPE to keep the body cool, administrative controls to limit exposure to the heat, and a good supply of fluids.

Whether you’re dealing with heat stress or heat-related illnesses, it’s all about staying cool, staying hydrated, and staying safe.

Ready to learn more? Check out our free webinar: 3 Steps to an Impactful Heat Stress Prevention Program!

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Written by Safeopedia Staff

Safeopedia Staff

At Safeopedia, we think safety professionals are unsung superheroes in many workplaces. We aim to support and celebrate these professionals and the work they do by providing easy access to occupational health and safety information, and by reinforcing safe work practices.

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