Brian Bossak, College of Charleston

Beach trips, cookouts and other outdoor activities are in full swing as summer arrives and the first widespread heat wave of 2025 hits the U.S.

For many people, summer is their favorite time of year. However, summer also brings the risk of dangerously high temperatures.

In the U.S., hundreds of people working or playing outside – even those who seem healthy – succumb to heat-related illnesses each year. Older adults and people in areas that historically haven’t needed air conditioning tend to see the highest rates of illnesses during heat waves, as Chicago saw in 1995 when at least 700 people died in a heat wave.

Even in places where heat is recognized as a dangerous health threat, people can be caught off guard as the thermometer creeps higher, on average, each year. In some cases, dangerous heat can arise quickly. In 2021, a young family died of heat stroke on a California trail after setting out for a hike when temperatures were still in the 70s Fahrenheit (low to mid 20s Celsius).

I study health risks in a warming climate as a professor of public health, and I’ve seen heat become a growing concern. Here are some of the key warning signs to watch for when temperatures rise – and ways to keep cool when the heat and humidity get too high.

Signs of heat-related illness to watch for

Heat-related illnesses occur across a spectrum, and mild heat stress can quickly progress to life-threatening heat stroke if a person is exposed to dangerous conditions for too long.

Mild forms of heat-related illness include heat cramps and heat rash, both of which can be caused by extensive sweating during hot conditions. Cooling the body and drinking cool fluids can help.

When heat-related illnesses progress into heat exhaustion, the situation is more serious. Heat exhaustion includes symptoms such as dizziness, nausea, excessive sweating, feeling weak, thirst and getting a headache.

Heat exhaustion is a signal that the body is losing its ability to maintain a stable core temperature. Immediate action such as moving to a cool, ideally air-conditioned space, drinking liquids, loosening clothes and applying wet cloths are some of the recommended steps that can help keep heat exhaustion from progressing to the most dangerous form of heat-related illness, heat stroke.

Heat stroke is a medical emergency. At this point, the body can no longer maintain a stable core temperature. A body with heat stroke can reach 106 degrees Fahrenheit or higher rapidly, and that heat can quickly damage the brain, heart and kidneys.

Typically, someone suffering heat stroke has exhausted their reserves of sweat and salt to stay cool, so sweating eventually stops during heat stroke. Their cognitive ability fails, and they cannot remove themselves from danger. Heat stroke can cause seizures or put someone into a coma as their core temperature rises. If the condition is not treated immediately, and the core temperature continues to rise, heat stroke becomes fatal.

Because heat exhaustion can lead to heat stroke, addressing heat-related illnesses before they progress is vital.

How to tell when the heat is too high

Heat risk isn’t just about temperature – humidity also increases the risk of heat-related illnesses because it affects how well sweating will cool the human body when it gets hot.

Instead of just looking at temperature when planning outdoor activities, check the heat index, which accounts for heat illness risk associated with temperature and relative humidity.

It doesn’t take very high temperatures or very high humidity for the heat index to enter dangerous territory.

However, the heat index is still a conservative measure of the impact of heat on humans, particularly for outdoor workers and athletes at summer practices. This is because temperature measurements used in weather forecasting are taken in the shade and are not exposed to direct sunlight. If someone is outside and exposed to the direct sun, the actual heat index can be as much as 15 F higher than the heat index chart indicates.

A more sophisticated measurement of heat effects on human health is what’s known as the wet-bulb globe temperature, which takes into account other variables, such as wind speed and cloud cover. Neither takes into account a person’s physical exertion, which also raises their body temperature, whether working at a construction site or playing soccer.

Tips for staying safe in a heat wave

How can you stay cool when heat waves set in? The answer depends in part on where you are, but the main points are the same:

• Avoid strenuous outdoor activities in high temperatures if possible. If you start to feel symptoms of heat-related illnesses, drink fluids that will hydrate you. Find shade, rest, and use cool, damp cloths to lower your body temperature. If you see signs of heat stroke in someone else, call for medical help.

• Be careful with fans. Fans can be useful if the temperature isn’t too high because they wick sweat away from the body and induce evaporative cooling. But at very high temperatures, they can accelerate heat buildup in the body and lead to dangerous conditions. If indoor temperatures reaches 95 degrees or higher, using fans can actually be dangerous and raise the risk of heat-related illnesses.

• Find a cooling center, library or community center where you can get inside and rest in an air-conditioned space in the hottest hours. In places such as Phoenix, where high temperatures are a regular hazard, cooling centers are typically opened in summer. Northern cities are also opening cooling centers as heat waves occur there more frequently than they did in the past. Urban areas with a lot of pavement and buildings – known as heat islands – can have temperatures well above the city’s average.

• Hydrate, hydrate, hydrate! Drink plenty of fluids, and don’t forget about the importance of electrolytes. Heat-related dehydration can occur when people sweat excessively, losing water and necessary salts from the body. Some sports drinks or rehydration fluids restore electrolytes and hydration levels.

Older adults and people with disabilities often face higher risks from heat waves, particularly if they can’t easily move to a cooler environment. Communities and neighbors can help protect vulnerable populations by providing cooling centers and bottled water and making regular wellness checks during high heat.

Summer can be a season of fun. Just remember the risks, keep an eye on your friends and neighbors when temperatures rise, and plan ahead so you can beat the heat.

Brian Bossak, Professor of Public Health, College of Charleston

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Gareth J. Fraser, University of Florida

The summer of 1975 was the summer of “Jaws.”

The first blockbuster movie sent waves of panic and awe through audiences. “Jaws” – the tale of a killer great white shark that terrorizes a coastal tourist town – captured people’s imaginations and simultaneously created a widespread fear of the water.

To call Steven Spielberg’s masterpiece a creature feature is trite. Because the shark isn’t shown for most of the movie – mechanical difficulties meant production didn’t have one ready to use until later in the filming process – suspense and fear build. The movie unlocked in viewers an innate fear of the unknown, encouraging the idea that monsters lurk beneath the ocean’s surface, even in the shallows.

And because in 1975 marine scientists knew far less than we do now about sharks and their world, it was easy for the myth of the rogue shark as a murderous eating machine to take hold, along with the assumption that all sharks must be bloodthirsty, mindless killers.

But in addition to scaring many moviegoers that “it’s not safe to go in the water,” “Jaws” has over the years inspired generations of researchers, including me. The scientific curiosity sparked by this horror fish flick has helped reveal so much more about what lies beneath the waves than was known 50 years ago. My own research focuses on the secret lives of sharks, their evolution and development, and how people can benefit from the study of these enigmatic animals.

The business end of sharks: Their jaws and teeth

My own work has focused on perhaps the most terrifying aspect of these apex predators, the jaws and teeth. I study the development of shark teeth in embryos.

Sharks continue to make an unlimited supply of tooth replacements throughout life – it’s how they keep their bite constantly sharp.

Hard-shelled prey, such as mollusks and crustaceans, from sandy substrates can be more abrasive for teeth, requiring quicker replacement. Depending on the water temperature, the conveyor belt-like renewal of an entire row of teeth can take between nine and 70 days, for example, in nurse sharks, or much longer in larger sharks. In the great white, a full-row replacement can take an estimated 250 days. That’s still an advantage over humans – we never regrow damaged or worn-out adult teeth.

Interestingly, shark teeth are much like our own, developing from equivalent cells, patterned by the same genes, creating the same hard tissues, enamel and dentin. Sharks could potentially teach researchers how to master the process of tooth renewal. It would be huge for dentistry if scientists could use sharks to figure out how to engineer a new generation of teeth for human patients.

Extraordinary fish with extraordinary biology

As a group, sharks and their cartilaginous fish relatives – including skates, rays and chimaeras – are evolutionary relics that have inhabited the Earth’s oceans for over 400 million years. They’ve been around since long before human beings and most of the other animals on our planet today hit the scene, even before dinosaurs emerged.

Sharks have a vast array of super powers that scientists have only recently discovered.

Their electroreceptive pores, located around the head and jaws, have amazing sensory capabilities, allowing sharks to detect weak electrical fields emitted from hidden prey.

Their skin is protected with an armor of tiny teeth, called dermal denticles, composed of sensitive dentin, that also allows for better drag-reducing hydrodynamics. Biologists and engineers are also using this “shark skin technology” to design hydrodynamic and aerodynamic solutions for future fuel-efficient vehicles.

Some sharks are biofluorescent, meaning they emit light in different wavelengths after absorbing natural blue light. This emitted fluorescent color pattern suggests visual communication and recognition among members of the same species is possible in the dark depths.

Sharks can migrate across huge global distances. For example, a silky shark was recorded traveling 17,000 miles (over 27,000 kilometers) over a year and a half. Hammerhead sharks can even home in on the Earth’s magnetic field to help them navigate.

Greenland sharks exhibit a lengthy aging process and live for hundreds of years. Scientists estimated that one individual was 392 years old, give or take 120 years.

Still much about sharks remains mysterious. We know little about their breeding habits and locations of their nursery grounds. Conservation efforts are beginning to target the identification of shark nurseries as a way to manage and protect fragile populations.

Tagging programs and their “follow the shark” apps allow researchers to learn more about these animals’ lives and where they roam – highlighting the benefit of international collaboration and public engagement for conserving threatened shark populations.

Sharks under attack

Sharks are an incredible evolutionary success story. But they’re also vulnerable in the modern age of human-ocean interactions.

Sharks are an afterthought for the commercial fishing industry, but overfishing of other species can cause dramatic crashes in shark populations. Their late age of sexual maturity – as old as 15 to 20 years or more in larger species or potentially 150 years in Greenland sharks – along with slow growth, long gestation periods and complex social structures make shark populations fragile and less capable of quick recoveries.

Take the white shark (Carcharodon carcharias), for example – Jaws’ own species. Trophy hunting, trade in their body parts and commercial fishery impacts caused their numbers to dwindle. As a result, they received essential protections at the international level. In turn, their numbers have rebounded, especially around the United States, leading to a shift from critically endangered to vulnerable status worldwide. However, they remain critically endangered in Europe and the Mediterranean.

“Jaws” was filmed on the island of Martha’s Vineyard, in Massachusetts. After careful management and the designation of white sharks as a prohibited species in federal waters in 1997 and in Massachusetts in 2005, their populations have recovered well over recent years in response to more seals in the area and recovering fish stocks.

You might assume more sharks would mean more attacks, but that is not what we observe. Shark attacks have always been few and far between in Massachusetts and elsewhere, and they remain rare. It’s only a “Jaws”-perpetuated myth that sharks have a taste for humans. Sure, they might mistake a person for prey; for instance, surfers and swimmers can mimic the appearance of seals at the surface. Sharks in murky water might opportunistically take a test bite of what seem to be prey.

But these attacks are rare enough that people can shed their “Jaws”-driven irrational fears of sharks. Almost all sharks are timid, and the likelihood of an interaction – let alone a negative one – is incredibly rare. Importantly, there more than 500 species of sharks in the world’s oceans, each one a unique member of a particular ecosystem with a vital role. Sharks come in all shapes and sizes, and inhabit every ocean, both the shallow and deep-end ecosystems.

Most recorded human-shark interactions are awe-inspiring and not terrifying. Sharks don’t really care about people – at most they may be curious, but not hungry for human flesh. Whether or not “Jaws” fans have grown beyond the fear of movie monster sharks, we’re gonna need a bigger conservation effort to continue to protect these important ocean guardians.

Gareth J. Fraser, Associate Professor of Evolutionary Developmental Biology, University of Florida

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Jane Tavares, UMass Boston and Marc Cohen, UMass Boston

When you lose your health insurance or switch to a plan that skimps on preventive care, something critical breaks.

The connection to your primary care provider, usually a doctor, gets severed. You stop getting routine checkups. Warning signs get missed. Medical problems that could have been caught early become emergencies. And because emergencies are both dangerous and expensive, your health gets worse while your medical bills climb.

As gerontology researchers who study health and financial well-being in later life, we’ve analyzed how someone’s ties to the health care system strengthen or unravel depending on whether they have insurance coverage. What we’ve found is simple: Staying connected to a trusted doctor keeps you healthier and saves the system money. Breaking that link does just the opposite.

And that’s exactly what has us worried right now. Members of Congress are debating whether to make major cuts to Medicaid and other social safety net programs. If the Senate passes its own version of the tax-and-spending package that the House approved in May 2025, millions of Americans will soon face exactly this kind of disruption – with big consequences for their health and well-being.

How people end up uninsured

Someone can lose their health insurance for a number of reasons. For many Americans, coverage is tied to employment. Being fired, retiring before you turn 65 and become eligible to enroll in the Medicare program, or even getting a new job can mean losing insurance. Others wind up uninsured due to a different array of changes: moving to a different state, getting divorced or aging out of a parent’s plan after their 26th birthday.

And those who buy their own coverage may find that they can no longer afford the premiums. In 2024, average premiums on the individual market exceeded more than US$600 per month for many adults, even with subsidies.

Government-sponsored insurance programs can also leave you vulnerable to this predicament. The Senate is currently considering its own version of a tax-and-spending bill the House of Representatives passed in May that would make cuts and changes to Medicaid. If the provisions in the House bill are enacted, millions of Americans who get health insurance through Medicaid – a health insurance program jointly run by the federal government and the states that is mainly for people who have low incomes or disabilities – would lose their coverage, according to the nonpartisan Congressional Budget Office.

Consequences of becoming uninsured

Health insurance is more than a way to pay medical bills; it’s a doorway into the health care system itself. It connects people to health care providers who come to know their medical history, their medications and their personal circumstances.

When that door closes, the effects are immediate. Uninsured people are much less likely to have a usual source of care – typically a doctor or another primary care provider or clinic you know and trust. That relationship acts as a foundation for managing chronic conditions, staying current with preventive screenings and getting guidance when new symptoms arise.

Researchers have found that adults who go uninsured for even six months become significantly more likely to postpone care or forgo it altogether to save money. In practical terms, this means they’re less likely to be examined by someone who knows their medical history and can spot red flags early.

The Affordable Care Act, the landmark health care law enacted during the Obama administration, made the number of Americans without insurance plummet. The share of people without insurance fell from 16% in 2010 to 7.7% in 2023.

The people who got insurance coverage, particularly those who were middle age, saw big improvements in their health.

Researching the results

In research that looked at data collected from 2014 to 2020, we followed what happened to 12,000 adults who were 50 or older and lived across the nation.

Our research team analyzed how their experiences changed when they lost, and sometimes later regained, a regular source of care during those six years.

Many of the participants in this study had multiple chronic conditions like diabetes, hypertension and heart disease.

The results were striking.

Those who didn’t see the same provider on a regular basis were far less likely to feel heard or respected by health care professionals. They had fewer medical appointments, filled fewer prescriptions and were less likely to follow through with recommended treatments.

Their health also deteriorated considerably over the six years. Their blood pressure and blood sugar levels rose, and they had more elevated indicators of kidney impairment compared with their counterparts who had regular care providers.

The longer they went without consistent health care, the worse these clinical markers became.

Warning signs

Preventive care is one of the best tools that both patients and their health care providers have to head off major health problems. This care includes screenings like cholesterol and blood pressure checks, mammograms, PAP smears and prostate exams, as well as routine vaccinations. But most people only get preventive care when they stay engaged with the health care system.

And that’s far more likely when you have stable and comprehensive health insurance coverage.

Our research team also examined what happened to preventive care based on whether the participants had a regular doctor. We found that those who kept seeing the same providers were almost three times more likely to get basic preventive services than those who did not.

Over time, these missed preventive care opportunities can add up to a big problem. They can turn what could have been a manageable issue into an emergency room visit or a long, expensive hospital stay.

For example, imagine a man in his 50s who no longer gets cholesterol screenings after losing insurance coverage. Over several years, his undiagnosed high cholesterol leads to a heart attack that could have been prevented with early medication. Or a woman who skips mammograms because of out-of-pocket costs, only to face a late-stage cancer diagnosis that might have been caught years earlier.

Shifting the costs

Patients whose conditions take too long to be diagnosed aren’t the only ones who pay the price.

We also studied how stable care relationships affect health care spending. To do this, we linked Medicare claims cost data to our original study and tracked the medical costs of the same adults age 50 and older from 2014 to 2020. One of our key findings is that people with regular care providers were 38% less likely to incur above-average health care costs.

These savings aren’t just for patients – they ripple through the entire health care system. Primary care stability lowers costs for both public and private health insurers and, ultimately, for taxpayers.

But when people lose their health care coverage, those savings disappear.

Emergency rooms see more uninsured patients seeking care that could have been handled earlier and more cheaply in a clinic or doctor’s office. While hospitals are legally required to provide emergency care regardless of a patient’s ability to pay, much of the resulting cost goes unreimbursed.

Hospitals foot the bill for about two-thirds of those losses. They pass the other third along to private insurance companies through higher hospital fees. Those insurers, in turn, raise their customers’ premiums. Larger taxpayer subsidies can then be required to keep hospitals open.

Seeing Medicaid as a lifeline

For the nearly 80 million Americans enrolled in Medicaid, the program provides more than coverage.

It contributes to the health care stability our research shows is critical for good health. Medicaid makes it possible for many Americans with serious medical conditions to have a regular doctor, get routine preventive services and have someone to turn to when symptoms arise – even when they have low incomes. It helps prevent health care from becoming purely crisis-driven.

As Congress considers cutting Medicaid funding by hundreds of billions of dollars, we believe that lawmakers should realize that scaling back coverage would break the fragile links between millions of patients and the providers who know them best.

Jane Tavares, Senior Research Fellow and Lecturer of Gerontology, UMass Boston and Marc Cohen, Professor of Gerontology, UMass Boston

This article is republished from The Conversation under a Creative Commons license. Read the original article.