Summertime, for many in the US, is the best part of the year. Weeklong trips to the beach. Weekends spent lounging and grilling by the pool. And in the middle of it all, on July 4, one of the most festive holidays on the calendar.

Summer also brings with it heat. In some portions of the country, it can be oppressive.

Of course, mercury busting temperatures are nothing new during the months between June and August (considered meteorological summer). The hot US summers of 1936, 1980, and 1983 were record-breaking. Short, but incredibly deadly heat waves occurred in Los Angeles in 1955 (946 deaths) and New York in 1972 (891 deaths).

However, if it seems that in more recent years temperatures have been uncomfortably warm, you’re not mistaken. Of the ten hottest years in the US, the top four have all come within the past decade.

Let’s sweat it out a bit and look closer at heat – more specifically, heat waves – and what they can do to the human body and how to protect yourself when the temperature starts rising.

What is a Heat Wave?

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We all know summertime is hot. The seasonality of our climate dictates that temperatures push upward June through August across the US. It’s not uncommon for many parts of the south and southwest to experience triple-digit readings during this time.

A heat wave happens when high pressure creates a dome of air over a specific region. This dome traps air at ground level and prevents it from rising. Without this rising air, rain can’t develop, and there’s no mechanism to prevent the hot air from growing even hotter.

Until the dome of high-pressure moves or is displaced by another weather system, the blistering hot air remains in place.

As an example, let’s examine summers in Dallas, Texas.

Collectively, since the year 1994, Dallas’ average June through August temperature is 85°F. From the chart, you can see that in some months the average temperature topped out a few degrees higher, between 87°F and 89°F. This reflects daytime highs in the city that reached between 90°F and 99°F.

Hot, yes, but not uncommon, even if for an extended period.

In a heat wave, the temperature rises to a point well above the norm, doing so over a period of time. Prolonged bouts of heat can last several days, weeks, or, in the most extreme cases, months.

Again looking at the linked chart, you can spot several of the most notable Dallas heat waves in months where the average temperature exceeded 90 degrees.

In 2011 alone, Dallas saw two streaks of consecutive days over 100°F at 40 and 20 days, respectively, which was part of a two-plus month long heat wave that ultimately saw 70 days scorch past the century mark. Other heat waves in Dallas during our 25-year sample occurred in 1998, 1999, 2006, 2010, as well as another one just last year.

While a heat wave in a warm climate may not be an extraordinary weather occurrence, its anticipated that heat waves in general – and their severity – are expected to become more frequent as temperatures rise globally. This includes areas not typically associated with the sweltering heat of summer.

For instance, in August of 2003, nearly 70,000 people succumbed to stifling heat in Europe. In 2018, a heat wave across Japan was so severe, their government declared the soaring temperatures a natural disaster, with a spokesman proclaiming the weather “unprecedented” and “a threat to life.”

In the US, heat proves deadliest among weather-related fatalities. In 2018, heat was responsible for more deaths than floods, tornadoes, and hurricanes combined.

Intensification of a Heat Wave

There are several conditions which can intensify a heat wave. Should a dome of heat form in a climate unaccustomed to oppressively hot weather – where air conditioning proves the exception, not the rule – residents can endure oven-like temperatures within their homes during the daytime.

A city, by way of endless asphalt, concrete, and glass, may amp up the effects of a heat wave through a phenomenon known as “urban heat island.” The city retains the heat for more extended periods, which means nighttime temperatures remain high versus cooling off.

According to Jonathan Erdman, a meteorologist, it’s a deadly combination:

“Overnight temperatures which don’t drop below 80 degrees are dangerous because those without air conditioning can’t simply open their windows for relief at night. So, essentially, there’s no break in the heat at night.”

In other words, you don’t even have to be outside to endure the brunt of a heat wave and potentially fall victim to its harmful consequences.

Effects of Heat on the Human Body

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There’s no question that heat can be uncomfortable. Excessive heat can be unbearable.

Aside from the constant pounding of sunlight or the searing air that accompanies an outbreak of high temperatures, prolonged heat exposure can be life-threatening. Between agonizing symptoms and loss of bodily function, if overexposure to heat is left untreated, it will lead to death.

Here are five of the most common heat-related conditions and illnesses:


Dehydration results from our bodies losing more water than what is being put in.

Although dehydration happens in many non-heat related situations, exposure to heat will speed up the processes that lead to the condition. Often this occurs without the person who is suffering from dehydration realizing it before it’s too late.

In weather such as a heat wave, our bodies will sweat more than usual to combat the increased temperatures. The rapid increase in water loss leads to symptoms both minor – headaches, muscle cramps, thirst and dry mouth – and far more severe – dizziness, nausea, confusion, rapid heartbeat or breathing, and fainting.

Everyone is susceptible to dehydration. However, infants and young children, older adults, people with illnesses or chronic disease, and even otherwise healthy individuals with active outdoor lifestyles are most at risk.

Heat Cramp

The first of four conditions caused by the overheating of the body or hyperthermia, heat cramps develop through an excessive loss of fluids, salt, and other minerals. These cramps may be incredibly painful, lasting longer than non-heat related cramping.

Muscles most often impacted by heat cramp include those in your abdomen, arms, and calves. Individuals who exercise heavily, particularly in outdoor environments, are most susceptible.

Heat Rash

When you sweat, it helps cool your body’s overall temperature. When this sweat becomes trapped beneath blocked pores in your skin, it leads to an outbreak of light, red blistering.

The least critical of the heat-related illnesses, heat rash is nonetheless an uncomfortable condition. Larger blisters may form, and intense itching may accompany the rash depending on its severity.

Although the vast majority of cases clear up within a couple of days, the worst instances involve painful swelling of the skin or lymph nodes, pus discharging from the blisters, or fever or chills.

Heat Exhaustion

When suffering from heat exhaustion, it’s typically the first indication that your body is rapidly starting to overheat. Symptoms include profuse sweating, a very rapid or feeble pulse, dizziness, nausea, severe cramping, and headaches, or increased fatigue. You may also have skin that is cool and moist to the touch even if you are in hot conditions.

Heat exhaustion can occur simply from being in the heat for too long. Its onset may happen sooner if you are performing strenuous activity while in the heat or heat combined with humid conditions (high heat index). Rapid temperature changes can also cause exhaustion, especially for those not accustomed to warmer areas.

As with other heat-related conditions, young children and older adults may experience exhausting faster than others, though obesity can also accelerate exhaustion symptoms due to the body retaining heat.

Heat Stroke

When your body reaches critical levels of overheating, you can fall victim to heat stroke. The most serious of the heat-based illnesses, individuals that encounter heat stroke require immediate medical attention.

When the body faces prolonged exposure to excessive heat, the body’s core temperature rises. Heat stroke happens with that core number reaches or exceeds 104°F. Coupled with fluid loss (dehydration), your body can no longer regulate its temperature.

Symptoms can appear immediately and include nausea, vomiting, rapid heartbeat and breathing, inability to sweat, severe headache or light-headedness, or confusion and disorientation. An individual may also suffer from seizures and unconsciousness.

If not treated immediately – which involves lowering the body’s core temperature – heat stroke can be fatal.

Final Thoughts: How to Stay Cool During a Heatwave


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The world is getting hotter.

Increased temperatures indicate an increase in heat waves and with them, heat-related illnesses. Protecting yourself, however, is a relatively simple combination of diligence and common sense – practically all of which you have seen or heard before:

  • Drink plenty of fluids, and consume more when active or outside in the heat of the day. If you’re in a place with no clean water source, a water bottle with a built-in filter can keep you hydrated in unsafe conditions.
  • Be mindful of what your body is losing when it sweats – minerals – and take care to replace them through sports drinks or your diet.
  • Don’t overexert yourself and take frequent breaks if outside in excessive heat or even when physically active in average, summertime temps.
  • Wear sunscreen when outside (no matter the temperature) and choose appropriate clothes for the conditions – lightweight and light-colored.
  • If you don’t have to be outdoors in the heat, stay inside, preferably places with air conditioning; if you do have to be out during the summer, schedule your activities during the coolest stretches whenever possible.

We can’t escape the heat – experts predict it to become a more significant burden in the coming decades. Knowing the risks of scorching temperatures – and the heat waves they produce – allows you to take preventative measures to “beat the heat” long before it beats you.

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