Taking Tests in a Heat Wave is Not So Hot

Businesswoman Sweating At Work With Broken Conditioner

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You know the feeling: It’s like a sauna outside. Sweat pours down your face and body. You drink gallons of water and still can’t get cool. You don’t want to exert much physical effort. The dog days of summer are here, but with a heightened intensity. Record-breaking heat in the U.S.—with North Texas seeing triple digit temperatures for days on end and daytime highs in Southern California reaching 117 degrees F—along with soaring global temps put many people at risk for dehydration and heat stroke. It’s August and the heat is on.

A new study suggests that a heat-induced “muddled” brain can affect the way you learn—more so than just feeling uncomfortable. Researchers studied two groups of students during a heat wave. One group lived in air conditioned apartments that were cooled to 71 degrees F. The other group’s living spaces were not air conditioned and averaged about 80 degrees F. The students were given tests that assessed their math skills, speed, memory and attention as soon as they woke up for 12 days.

Students who lived in the air conditioned buildings answered more questions correctly and had faster response times than the students who lived in hotter buildings. The researchers noted that their study is just one more sign that heat stress can have a negative effect on the mind as well as the body. Although previous studies suggest that, in some cases, heat stress reduces blood flow to the brain, it’s unclear how heat impacts cognitive skills and scientists have much more to learn about the body’s response to extreme heat.

If you like the heat, it’s okay to soak up some rays and enjoy the warmth. Just remember to take steps to protect your skin and kidneys. And if you have test-taking in your future, make sure your air conditioner is working!

Erica Roth

Here Comes the Sun (and the Heat)

A thermometer shows high temperatures against the sun, a blue sky and a few white clouds.

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Summer is in full swing, and with a near-peak number of daylight hours, chances are good that there is still plenty of light left to enjoy once your workday is done. Before you get outside and bask in the sun and heat, check out these I Spy posts that explain how your body responds to hot weather and provide tips to help you stay safe this summer:

Have a safe, sunny and fun summer!

Erica Roth

Putting Out Fires Hurts Firefighters’ Hearts

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As the temperature outside rises, our bodies make adjustments to keep our internal temperature constant to prevent us from overheating through a process called thermoregulation. This includes bodily functions such as sweating and widening of the blood vessels (vasodilation). When we sweat, perspiration evaporates from our skin to cool us down. When the blood vessels under our skin widen, our heart pumps more blood to our skin, which releases more heat from our inner body.

Our bodies are constantly working to hold a steady core temperature around 98-100 degrees Fahrenheit (F). This allows our organs to function properly. But when the temperature outside is extremely hot, our temperature can start to rise. A person with a body temperature above 104 degrees can develop heat stroke. This can cause dizziness, difficulty breathing, confusion, seizures or loss of consciousness. Brain and heart damage—sometimes permanent—can occur when body temperature climbs above 107 degrees F.

Too much summer heat can be unhealthy for everyone, but it can be especially dangerous to firefighters. The incidence of fires increases in the U. S. during the summer months. Firefighters fight almost twice as many fires in the summer compared to the rest of the year. On top of dealing with the extreme heat (sometimes over 700 degrees F!), these first responders face extreme physical exertion, mental stress and smoke inhalation on the job. All of these factors together can place firefighters in immediate danger of heat exhaustion, heatstroke and heart problems. In fact, firefighters are up to 136 times more likely to die of coronary artery or heart disease during or soon after they suppress a fire.

In a study published in Circulation last month, researchers may have uncovered several reasons why putting out fires puts firefighters at risk for heart disease. They discovered that a single, 20-minute session of fire simulation training—where healthy firefighters were exposed to physical activity in the extreme heat (about 755 degrees F)—was enough to injure their blood vessels, even though the firefighters’ core body temperature never reached above 101 degrees F. The problem: Although the firefighters’ bodies did keep their core temperature within a healthy range, their blood vessels did not relax properly immediately after the training. Also, as a result of the training, the firefighters’ blood clotted more easily. Damaged blood vessels and increased clotting of the blood can be very harmful to the heart and sometimes can lead to a heart attack.

This research shows us that even when we are able to keep our body temperature from getting too high, there are hidden dangers of being physically active in extremely hot temperatures. So keep your heart healthy this summer and don’t overexert yourself while outdoors!

Dao Ho, PhD

Dao H. Ho, PhD, is a biomedical research physiologist at Tripler Army Medical Center. The views expressed in this blog post are those of the author and do not reflect the official policy or position of the U.S. Department of the Army, U.S. Department of Defense or the U.S. government.

What Happens during Heat Stroke and How to Prevent It


Young kids are at increased risk of heat stroke. Credit: IStock

Temperatures in July and August 2016 were the hottest ever recorded on the planet and much of the U.S. is still struggling with a heat wave. Hundreds of heat-related deaths occur in the U.S. each year, and these rates are on the rise. Awareness of when the body is losing the ability to deal with heat and seeking treatment for heat illness and dehydration are key to reducing heat stroke-related deaths. So it’s extremely important to understand the causes and symptoms of heat illnesses, such as heat stroke, and who’s at risk.

Under normal physiologic conditions, the human body can counteract overheating by sweating and other means. Heat illness occurs when the body is overwhelmed by the heat and can no longer maintain its temperature. Heat stroke is the most dangerous type of heat illness, though heat fatigue, heat cramps and heat exhaustion can also occur. These conditions can have a variety of effects on the body, blood flow and a person’s mental capacity. For example, heat stress with mild to moderate dehydration can result in loss of blood flow to the brain and the inability to stay upright.

Who’s at Risk of Heat Stroke and How to Prevent It

Heat stroke can develop in people of any age or health status, but the sedentary elderly, very young people and individuals with chronic disease such as heart disease have a significantly higher risk of having one. People who take certain medications, drink alcohol, are very overweight or who have poor blood circulation (such as those with diabetes and heart disease) or reduced sweat production due to aging are also at an increased risk. Prolonged, intense exercise in a hot environment without proper hydration can cause a heat stroke during heat waves, even among young and healthy people.

The most effective ways to prevent heat stroke is to ensure that high-risk populations:

  • have access to air conditioning or a cool environment with air flow;
  • dress comfortably in layers that can be removed as the temperature rises;
  • stay hydrated by consuming water, fruits and vegetables (such as watermelon, tomatoes, lettuce, pineapple, cranberries and oranges), herbal tea, etc; and
  • understand the signs and symptoms of heat stroke.

People may be developing heat illness if they appear confused or faint, are not sweating or have flushed skin after being exposed to the heat. Any individual experiencing these symptoms should be removed from the heat, offered fluids and examined for the possibility of heat illness or heat stroke.


Robert Carter, III, PhD, MPH, FACSM, is an adjunct professor of emergency medicine at the University of Texas Health Science Center at San Antonio and the product manager for medical simulation at the Program Executive Office for Simulation, Training and Instrumentation in Orlando.

How Long Can You Hold Your Breath? The Dangers of Freediving

Freediver 2

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The appeal of freediving may lie in its freedom. Freedivers, without cumbersome scuba gear and noisy regulators, easily glide through tranquil waters toward coral or rocky reefs with scenes unobstructed by bubble trails. With dives often exceeding five minutes, they get to see up close and personal the colorful marine life that typically flees from noisy scuba divers. Freedivers can extend their time underwater by hyperventilating—breathing in and out rapidly—before diving. This allows more oxygen into the lungs, but if the dive is not planned and executed well, it can also have dangerous results.

Oxygen is key to our survival: It’s used to make ATP, a molecule that fuels everything we do. When we breathe in, oxygen in the air travels into our lungs, goes into our blood and finally makes it to our cells, where ATP is produced. Carbon dioxide (CO2) is also made during ATP production. As we make more and more ATP, CO2 builds up. To get rid of this accumulated CO2, CO2 flows from the cells to the blood and then into the lungs, where we eventually exhale it.

The presence of CO2 in our lungs means there is less room for oxygen. Hyperventilating can cut the amount of CO2 in half, allowing more space for oxygen. With this additional oxygen, freedivers can stay underwater a little longer, but they can misjudge when they need to head to the surface for air.

Low oxygen level is not what prompts us to breathe. Rather it’s the accumulation of CO2. Under normal breathing, the buildup of CO2 signals us to breathe before oxygen becomes too low. However, hyperventilating reduces CO2, and the signal to breathe comes later. Without a timely signal, a freediver may dive too long and allow too much oxygen to be consumed. As the diver finally heads to the surface, oxygen can become too low for the brain to maintain consciousness. The consequences can be fatal.

Cassondra Williams


Cassondra Williams, PhD, is a postdoctoral fellow at Scripps Institution of Oceanography.

No More Motion Sickness! Tips for Finding Your Steady State

Bill Yates, PhD

Bill Yates, PhD

Summer vacation season brings distress to a number of people who suffer from motion sickness. Motion sickness causes a variety of symptoms, including queasiness, sweating and pale skin color. Some people also experience fatigue and, occasionally, vomiting.

We still don’t know why people get motion sickness, but the circumstances that produce the condition are well known. Motion sickness occurs when the brain receives input about the orientation and movement of the body that differ from those that are expected. For example, when reading a book in a car, our eyes tell us that the body is not moving while receptors in the inner ear, which are part of the vestibular system, tell the brain that the movement is occurring. These contradictory senses can trigger motion sickness. However, we don’t have to be moving to get motion sick. People watching a movie can get motion sick, too, as movement on the screen signals to their brain that they are moving, but the vestibular system tells them they are stationary.

Input from the inner ear seems to be a key component in producing motion sickness, as people with damage to the inner ear on both sides cannot be made motion sick. Some people are also more likely to get motion sick than others, such as those who suffer from frequent migraine headaches.

How can you prevent motion sickness? A number of drugs have been used to treat the condition, including over-the-counter medications such as Dramamine.  But these medications tend to cause drowsiness. Other treatments, such as wristbands that apply pressure at acupressure points are available, and some people claim they work well. However, most scientists think that such treatments provide only a “placebo effect”: the patient expects to feel better, and thus they claim that they do.

Perhaps the simplest treatment for motion sickness is avoiding the misleading sensory cues that produce the condition. Drivers of vehicles rarely get motion sick because they focus on the road and get both visual and vestibular cues that they are moving. People on boats or planes tend not to get motion sick if they look to the horizon instead of focusing on the inside of the vehicle. If you don’t confuse your brain about your movement, then travel will be more enjoyable!

Bill Yates, PhD, is a professor of otolaryngology and neuroscience and clinical and translational science at the University of Pittsburgh. He is also editor-in-chief of the Journal of Neurophysiology.

Stop Scratching! Why Mosquito Bites Swell and Itch

Close up a Mosquito sucking human blood_set B-4

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It starts with a buzz and then a nip. If you’re quick enough, the culprit mosquito becomes a squashed smear on your hand. More often, it flies off unscathed. Either way, you’re left with a red, itchy welt. What physiological processes are set off to leave us swollen and uncomfortable when mosquitos bite?

It’s actually a misconception that all mosquitos bite to get blood. Only female mosquitos feed on blood, and they don’t bite to do it. They use their straw-like mouths to pierce through the skin to locate a blood vessel (Check out this video to see the mosquito’s mouth in action). After the mosquito hits one, she spits into the wound. The saliva contains proteins that prevent blood from clotting, allowing her to drink your blood freely. When the mosquito flies away, some of the saliva is left behind and triggers an immune response.

The immune system releases a substance called histamine that makes blood vessels around the bite enlarged and leaky. The increase in blood flow makes the bite appear red, and the flow of immune cells and fluid from the blood vessel into the surrounding area make the bite swell. Histamines also irritate the nerves in the bite area, making it itch.

As summer begins to wind down, mosquitos do, too. Avoid pools of standing water and shaded humid areas during the day, stay indoors from dusk to dawn and consider bug repellent to keep new bites away.  And, don’t scratch the bites you already have. Scratching can break the skin, which can cause infection and scars. End the summer itch-free!

Maggie KuoMaggie Kuo, PhD, is the former Communications and Social Media Coordinator for APS. Catch more of her writing in the Careers Section of Science Magazine.

Does Exercising in Warm Weather Make You Fitter for Cooler Temperature?

Hot Weather Exercise

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Those who are active year-round know that summer workouts are more tiring than those done in cooler weather. The good news is that it’s not a sign that you’re suddenly out of shape. Exercising in warm temperatures is not the same as exercising in cooler temperatures and the body’s physiology has to adjust. How does the body adapt and can these changes translate to performance gains in cooler temperatures?

The body takes about 10 days to acclimate to exercising in heat. The most noticeable signs that it has adapted to warmer weather are sweating more easily and a lower exercising heart rate. Less perceptible physiological changes include greater volume of plasma—the liquid portion of the blood in which the red blood cells are suspended—less salt released through sweat and more efficient heart and muscle function.

Because these physiological adaptations improve exercise performance in heat, scientists and athletes have wondered if these changes also mean enhanced performance in cool conditions. The jury, though, is still out. A study in 2010 in the Journal of Applied Physiology reported that exercising in heat did improve exercise performance in cooler weather. A new study published last month in the American Journal of Physiology—Heart and Circulatory Physiology concluded the opposite: heat training only improved performance in hot conditions, but not temperate ones. Nonetheless, both studies show that the body can adapt to new conditions relatively quickly. So, when you find it hard to catch up when it’s hot, be patient. You’re not out of shape, it’s just your body is catching up.

Maggie KuoMaggie Kuo, PhD, is the former Communications and Social Media Coordinator for APS. Catch more of her writing in the Careers Section of Science Magazine.

Soak Up the Rays without Soaking Them In: Be Sun Safe and Prevent Skin Damage


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Tan lines and sunburns are our souvenirs of summer. Unfortunately, they’re also reminders that we’ve had too much sun and the sun has damaged our skin. How does sun exposure harm skin, and what are the physiological processes that make us tan and burn?

The sun gives off a kind of radiation called ultraviolet (UV) radiation. Two types of UV radiation cause skin damage: UVA, which makes skin tan and wrinkle, and UVB, which causes sunburns. Both harm skin by damaging the DNA in skin cells. Too much DNA damage can lead to skin cancer.

Tanning is the first sign of sun damage. Skin cells produce a pigment called melanin, which gives skin its color and helps protect the skin by absorbing UV radiation. When the body senses UV damage, it tries to stop further damage by stimulating the skin cells to produce more melanin. Skin darkens as a result.

If there is too much DNA damage, the skin becomes inflamed and shows the signs of sunburn. Blood vessels in the sunburned area dilate and more blood flows through, making the skin appear red and feel hot. The immune system also releases chemicals that make the sunburnt skin swell and hurt. The skin peels to get rid of the damaged cells.

Although melanin absorbs UV rays, it’s not enough to protect you from burning or other skin damage. The extra melanin in tanned skin only comes in at the SPF 2 to 4 range. The minimum SPF recommendation is 15. To protect your skin, the American Cancer Society says to slip, slop, slap and wrap: Slip on a shirt, slop on sunscreen, slap on a hat and wrap on sunglasses. Keep these guidelines in mind when you’re headed outdoors for time under the sun. Take back the memories, but not the sun!

Maggie KuoMaggie Kuo, PhD, is the former Communications and Social Media Coordinator for APS. Catch more of her writing in the Careers Section of Science Magazine.

Reduce Your Risk of a “Lung Sunburn”: Stay Inside on Poor Air Quality Days


June 21 officially marked the first day of summer, bringing in long hot days of fun in the sun. Summer is also the time when air quality alerts start popping up, warning us to avoid breathing in bad air and limit activities outside. These alerts can put a damper on our outdoor plans, but why is poor air quality unhealthy for lung physiology?

The inside surface of our lungs is covered by a fluid called lung-lining fluid that helps keep the lungs clean. The fluid traps pollutants and particles, which are swept out by fine hairs that also line the lungs. Cells from the immune system drift around in the fluid, too. These cells can neutralize pollutants by ingesting and destroying them.

Air quality alerts are triggered by high levels of particulates and a chemical called ozone. When the temperature heats up, exhaust from cars, power plants and other sources turns into ozone. This is the same molecule making up the ozone layer that shields Earth from the sun’s radiation. Ozone high above protects our health, but on the ground, it can worsen it. Ozone dissolves in the lung-lining fluid, reacting with molecules in the fluid and on the surface of the lungs’ cells. The lung cells react by releasing molecules that attract and activate immune cells, leading to inflammation.

The American Lung Association describes ozone’s effect like a sunburn in the lungs. Symptoms of breathing in too much ozone include coughing, shortness of breath and difficulty breathing. The effects of ozone may be more severe among children and the elderly and in people with respiratory ailments such as asthma. The good news is that these effects are reversible and if you stop breathing ozone, symptoms can improve in a few hours. So, mind the poor air quality warning when you see it. Avoiding bad air is good for you and your lungs!

Maggie KuoMaggie Kuo, PhD, is the former Communications and Social Media Coordinator for APS. Catch more of her writing in the Careers Section of Science Magazine.