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Mosquitoes are not just a buzzing summertime nuisance; they can carry serious diseases like West Nile virus, malaria, and Zika. In recent months, the US has seen an unusual spike in the mosquito-borne illness dengue fever, also known as breakbone fever.

What is dengue, and where is it occurring in the US? How does it spread? And what steps can you take to protect against this and other mosquito-borne illnesses?

What is dengue and what are its symptoms?

Dengue is a viral disease caused by any of four closely-related viruses: dengue virus 1, 2, 3, and 4. Not everyone infected with dengue will become sick: only about one in four will experience symptoms that range from minimal discomfort to serious problems. A blood test is used to confirm the diagnosis.

When symptoms do occur, they tend to feel like the flu. The onset of feeling unwell usually begins within two to three days of being bitten by an infected mosquito but can take up to six to nine days, says Dr. Edward Ryan, director of global infectious diseases at Harvard-affiliated Massachusetts General Hospital.

Seek medical advice if you have recently traveled to an area with a risk of dengue and have a fever (101° F or higher) combined with any of these symptoms:

• aches and pains (often headache or pain behind the eye or in muscles, joints, or bones)
• nausea and vomiting
• a rash (faint red blotches).

About one in 20 people who gets sick will develop severe dengue, which requires emergency care. Those at an increased risk for severe dengue include infants a year or younger, pregnant women, adults ages 65 years or older, and those with previous dengue infections.

Symptoms of severe dengue require immediate medical care. They include:

• feeling very weak and lightheaded from low blood pressure
• bleeding from the nose or gums
• stomach swelling
• vomiting
• extreme fatigue.

How is dengue treated?

Dengue is cause by a virus, and no specific medications are available to combat it. Milder dengue symptoms typically last two to seven days, according to the Centers for Disease Control and Prevention (CDC). The symptoms are managed supportively: plenty of fluids, over-the-counter pain medications, and rest.

Severe dengue usually requires treatment in a hospital with intravenous (IV) fluids. Patients are monitored until their fever breaks and symptoms begin to wane. This usually happens in about three to five days. Recovery at home can last many more days before a person’s strength returns.

“While there are reports of people dying from severe dengue fever, deaths from dengue cases in the US are rare,” says Dr. Ryan.

How does dengue spread?

The viruses that cause dengue do not directly spread from person to person. Aedes species mosquitoes can become infected with the dengue virus when they bite a person who has the virus. Infected mosquitoes then spread the virus to other people.

US visitors to high-risk countries may unknowingly bring the virus home with them, giving dengue infection a chance to spread further. For example, an infected person will have dengue virus circulating in their bloodstream for up to one week after being bitten. Let’s say the person returns to the US sooner than seven days, where they get bitten by a mosquito. That mosquito in the US now carries the virus and could bite someone else, thereby spreading the infection.

Where is dengue occurring in the US?

Most dengue transmission in the United States happens in areas where this illness is already common, such as Puerto Rico, American Samoa, and the US Virgin Islands.

At this writing, the CDC has reported nearly 3,000 dengue cases in the United States and US territories. States with the highest reported instances include Florida, New York, Massachusetts, and California. (Puerto Rico, which declared a public health emergency in March, had reported almost 1,500 cases by late June 2024.) While US cases are higher than in previous years, they are still low compared to the global incidence of dengue, which hit a record 9.7 million cases in North, Central, and South America during the first six months of 2024.

It’s not clear what has caused the sudden rise in dengue cases. Dr. Ryan says it could be due to several factors, such as higher seasonal travel, more people living closer together in urban settings, and the fact that there are more mosquitoes are carrying dengue.

Is there a dengue vaccine?

Currently, there is no widely available dengue vaccine for US travelers. One FDA-approved vaccine, Dengvaxia, protects children ages 9 to 16 from all four types of dengue. It is used only for children who have had a previous infection and who live in areas where dengue is common. However, the vaccine will be discontinued in September 2025, with the final doses expiring in September 2026.

What steps can you take to prevent dengue?

The best way to prevent dengue when visiting high-risk areas and after returning home is to protect yourself from mosquito bites. Here are some tips from the CDC:

• Use EPA-registered insect repellents with one of the following active ingredients: DEET; picaridin (known as KBR 3023 and icaridin outside the United States); IR3535; oil of lemon eucalyptus (OLE) or 2-undecanone (plant-derived ingredients); or para-menthane-diol (PMD).
• Wear loose-fitting, long-sleeved shirts and pants.
• Wear clothing and gear treated with permethrin (an insecticide that kills or repels mosquitoes).
• Place screens on windows and doors.
• When traveling, stay in places with air conditioning and screens. Use a bed net if air-conditioned or screened rooms are unavailable or if sleeping outdoors.
• To prevent mosquitoes from laying eggs in or near water around your home, empty and scrub, turn over, cover, or throw out outdoor items that hold water. This includes tires, buckets, toys, kid pools, birdbaths, flower pot saucers, or trash containers.

About the Author

Matthew Solan, Executive Editor, Harvard Men's Health Watch

Matthew Solan is the executive editor of Harvard Men’s Health Watch. He previously served as executive editor for UCLA Health’s Healthy Years and as a contributor to Duke Medicine’s Health News and Weill Cornell Medical College’s … See Full Bio View all posts by Matthew Solan

About the Reviewer

Howard E. LeWine, MD, Chief Medical Editor, Harvard Health Publishing

Dr. Howard LeWine is a practicing internist at Brigham and Women’s Hospital in Boston, Chief Medical Editor at Harvard Health Publishing, and editor in chief of Harvard Men’s Health Watch. See Full Bio View all posts by Howard E. LeWine, MD

Ever wonder if every medical test or treatment you've taken was truly necessary? Or are you inclined to get every bit of health care you can? Maybe you feel good about getting the most out of your health insurance. Perhaps a neighborhood imaging center is advertising discounted screening tests, your employer offers health screens as a perk, or you're intrigued by ads touting supplements for a seemingly endless number of conditions.

But keep in mind: just because you could get a particular test or treatment or take a supplement doesn't mean you should. One study suggests that as much as 20% of all health care in the US is unneeded. In short: when it comes to health care, more is not always better.

Isn't it better to be proactive about your health?

We're all taught that knowledge is power. So it might seem reasonable to want to know as much as possible about how your body is working. And isn't it better to take action before there's a problem rather than waiting for one to develop? What's the harm of erring on the side of more rather than less?

The truth is that knowledge is not always power: if the information is irrelevant to your specific situation, redundant, or inaccurate, the knowledge gained through unnecessary health care can be unhelpful or even harmful. Unnecessary tests, treatments, and supplements come with risks, even when they seem harmless. And, of course, unnecessary care is not free — even if you're not paying a cent out of pocket, it drives up costs across health systems.

Screening tests, wellness strategies, and treatments to reconsider

Recommended screening tests, treatments, and supplements can be essential to good health. But when risks of harm outweigh benefits — or if proof of any benefit is lacking — think twice. Save your time, money, and effort for health care that is focused on the most important health threats and backed by evidence.

Cancer screening: When to stop?

Screening tests for some cancers are routinely recommended and can be lifesaving. But there's a reason they come with a recommended stop age. For instance, guidelines recommend that a person at average risk of colorectal cancer with previously normal colonoscopies stop having them once they turn 75. Similar limits apply to Pap smears (age 65) and mammograms (age 75). Studies suggest that beyond those ages, there is little benefit to continuing these screens.

Watch out for wellness marketing

Dietary supplements are a multibillion-dollar industry. And a whopping 70% or more of US adults take at least one, such as vitamin D, fish oil, or a multivitamin. People often consider them as insurance in case vital elements are missing from their diet, or they believe supplements can prevent dementia, heart disease, or another condition.

Yet little evidence supports a benefit of routine supplement use for everyone. While recent studies suggest a daily multivitamin might slow cognitive decline in older adults, there's no medical consensus that everyone should be taking a multivitamin. Fish oil (omega-3) supplements haven't proven to be as healthful as simply eating servings of fatty fish and other seafood low in toxic chemicals like mercury and PCBs. And the benefits of routinely taking vitamin D supplements remain unproven as well.

It's worth emphasizing that dietary supplements clearly provide significant benefit for some people, and may be recommended by your doctor accordingly. For example, if you have a vitamin or mineral deficiency or a condition like age-related macular degeneration, good evidence supports taking specific supplements.

Reconsider daily aspirin

Who should be taking low-dose aspirin regularly? Recommendations have changed in recent years, so this is worth revisiting with your health care team.

• Older recommendations favored daily low-dose aspirin to help prevent cardiovascular disease, including first instances of heart attack and stroke.
• New recommendations favor low-dose aspirin for people who've already experienced a heart attack, stroke, or other cardiovascular disease. Adults ages 40 to 59 who are at a high risk for these conditions and low risk for bleeding also may consider it.

Yet according to a recent study, nearly one-third of adults 60 and older without past cardiovascular disease take aspirin, despite evidence that it provides little benefit for those at average or low risk. Aspirin can cause stomach bleeding and raise risk for a certain type of stroke.

Weigh in on prostate cancer screening

Men hear about prostate cancer often. It's common, and the second leading cause of cancer deaths among men. But PSA blood tests and rectal exams to identify evidence of cancer in the prostate are no longer routinely recommended for men ages 55 to 69 by the United States Preventative Services Task Force.

The reason? Studies suggest that performing these tests does not reliably reduce suffering or prolong life. Nor do possible benefits offset downsides like false positives (test results that are abnormal despite the absence of cancer). That can lead to additional testing, some of which is invasive.

Current guidelines suggest making a shared decision with your doctor about whether to have PSA testing after reviewing the pros and cons. For men over age 70, no screening is recommended. Despite this, millions of men have PSA tests and rectal examinations routinely.

Not everyone needs heart tests

There are now more ways than ever to evaluate the health of your heart. But none are routinely recommended if you're at low risk and have no signs or symptoms of cardiovascular disease. That's right: in the absence of symptoms or a high risk of cardiovascular disease, it's generally safe to skip EKGs, stress tests, and other cardiac tests.

Yet many people have these tests as part of their routine care. Why is this a problem? Having these tests without a compelling reason comes with risks, especially false positive results that can lead to invasive testing and unneeded treatment.

Four more reasons to avoid unnecessary care

Besides the concerns mentioned already, there are other reasons to avoid unnecessary care, including:

• The discomfort or complications of testing. If you're needle-phobic, getting a blood test is a big deal. And while complications of noninvasive testing are rare (such as a skin infection from a blood test), they can occur.
• The anxiety associated with waiting to find out test results
• False reassurance that comes with false negatives (results that are normal or nearly so, suggesting no disease when disease is actually present)
• All treatments have side effects. Even minor reactions — like occasional nausea or constipation — seem unacceptable if there's no reason to expect benefit from treatment.

The bottom line

You may believe your doctor wants you to continue with your current schedule of tests and treatments, while they might think this is your preference! It's worth discussing if you haven't already, especially if you suspect you may be taking pills or getting tests you don't truly need.

If your doctor says you can safely skip certain tests, treatments, and supplements, it doesn't mean that he or she is neglecting your health or that you don't deserve great health care! It's likely that the balance of risks and benefits simply doesn't support doing these things.

Less unnecessary care could free up resources for those who need it most. And it could save you time, money, and unnecessary risks or side effects, thus improving your health. It's a good example of how less can truly be more.

About the Author

Robert H. Shmerling, MD, Senior Faculty Editor, Harvard Health Publishing; Editorial Advisory Board Member, Harvard Health Publishing

Dr. Robert H. Shmerling is the former clinical chief of the division of rheumatology at Beth Israel Deaconess Medical Center (BIDMC), and is a current member of the corresponding faculty in medicine at Harvard Medical School. … See Full Bio View all posts by Robert H. Shmerling, MD

Months after actor and comedian Robin Williams took his own life in August 2014, autopsy results revealed he had a devastating disease: Lewy body dementia (LBD). Unlike Alzheimer’s disease and even frontotemporal dementia, this brain disorder has tended to hide in the shadows. But work is underway to change that, says Dr. Stephen Gomperts, an assistant professor of neurology at Harvard Medical School and director of the Lewy Body Dementia Unit at Harvard-affiliated Massachusetts General Hospital.

Perhaps surprisingly, LBD is the second most common cause of neurodegenerative dementia after Alzheimer’s disease. How do its symptoms differ? Who is at risk? And how is it diagnosed and treated?

What is Lewy body dementia?

First, it’s important to know that there are two main types of this dementia. One is called dementia with Lewy bodies, or DLB. A second type, known as Parkinson’s disease dementia, or PDD, may arise late in the course of that illness.

These disorders stem from an abnormal buildup of protein deposits in the brain called Lewy bodies. The deposits, formed from a protein called alpha-synuclein, settle in brain areas affecting thinking, behavior, perception, and movement.

Much like Alzheimer’s disease, LBD is progressive and ultimately fatal. But while the median lifespan of people who have this illness is seven years, there is a high degree of variation in the duration of disease, says Dr. Gomperts. “Many people respond well to medicines that aim to improve their ability to function and quality of life.”

How common is it?

More than a million Americans live with Lewy body dementia. Others who likely have the disease may not have sought care or have been misdiagnosed, Dr. Gomperts says. “In the past, LBD was often subsumed under the general umbrella of ‘dementia’ or ‘Alzheimer’s.’ It’s still significantly underdiagnosed, but that’s getting better.”

Most people with LBD develop symptoms after age 50, so the numbers are likely to grow as the population continues to age.

How is Lewy body dementia similar to Alzheimer’s disease?

As with Alzheimer’s, LBD affects a person’s ability to think clearly, remember details, solve problems, focus on tasks, and eventually to care for themselves. “Gradually progressive trouble with thinking is the key shared feature between the two. This initially doesn’t impact activities of daily living, but ultimately it does,” he explains.

How does Lewy body dementia differ from Alzheimer’s disease?

In Alzheimer’s disease, memory problems usually occur early and are the dominant problem. In contrast, in LBD, difficulties with problem-solving or spatial problems tend to arise before memory difficulties. But any of these symptoms can occur first or in combination, and they may fluctuate. Perception is often affected, which can manifest as visual hallucinations. Delusions (false beliefs) are also common as the disease progresses.

“Whereas hallucinations and delusions are common late in the course of Alzheimer’s disease, visual hallucinations often arise early in LBD. For example, a person with LBD might see people or animals that aren’t there,” he says. “Such hallucinations are only rarely perceived as threatening.”

Other differences are:

• Acting out dreams. People with LBD may act out their dreams. Known as REM sleep behavioral disorder, this problem often arises even before thinking problems start.
• Changes in movement. People with Lewy body dementia often move slowly and stiffly, developing tremors and gait changes and becoming prone to falls. When people have PDD, progressive movement problems arise early and are the rule. This symptom leads to the initial diagnosis of Parkinson’s disease. In DLB, movement is often but not always affected.

How do experts distinguish between PDD and DLB?

It’s all in the timing of key symptoms. A “one-year rule” distinguishes each disorder.

• PDD: When someone diagnosed with Parkinson’s develops memory and thinking problems that impair activities of daily living more than a year after their movement problems arise, PDD is diagnosed.
• DLB: When cognitive problems arise earlier, or come without movement problems, dementia with Lewy bodies is diagnosed.

“But this one-year rule is somewhat arbitrary,” Dr. Gomperts says. “Increasingly we think of this as a spectrum of disease.”

Who is at risk for Lewy body dementia?

Age is considered the biggest risk factor for the disease. Most cases have no known trigger, although a handful of gene mutations can predispose someone to LBD.

Several lifestyle factors such as diet, lack of exercise, and toxic exposures have been linked to Parkinson’s disease risk. However, little research has been done to examine whether these factors are linked to LBD. People who have suffered head trauma appear to develop LBD and Parkinson’s more often. Both conditions also disproportionately affect men. “We think that’s telling us something important, but it’s not yet clear what,” Dr. Gomperts says.

How is Lewy body dementia diagnosed?

The diagnosis of DLB is made when key clinical features are present — trouble thinking, fluctuations in thinking, movement problems, and REM sleep behavioral disorder — in the absence of other causes. The diagnosis of PDD is made when dementia arises in Parkinson’s disease.

Diagnosing DLB is challenging because early symptoms are often confused with symptoms that arise in other brain or psychiatric disorders. Many people don’t receive an accurate diagnosis until their symptoms become more advanced, Dr. Gomperts says.

An array of tests and imaging exams is deployed to tease out LBD from other conditions that can trigger similar symptoms, such as Alzheimer’s disease, vascular disease, thyroid disorders, or vitamin B12 deficiency.

“Not all cases are clear-cut and not all physicians are skilled at making the diagnosis,” he says. “Accuracy is also lower in early disease.”

Are there treatments for Lewy body dementia?

Yes. Although there’s no cure, treatments like medications, physical therapy, and counseling can help with specific symptoms of LBD, such as thinking problems, hallucinations, and sleep disturbances. LBD-related movement symptoms can also be treated with some medications used for Parkinson’s. This makes it easier to walk and do other activities.

“We’ve also learned that several medications can cause or worsen certain symptoms, such as confusion, delusions, hallucinations, and movement problems,” Dr. Gomperts says. “In fact, some medications that target hallucinations and delusions often worsen motor function and can even be fatal in LBD. They need to be avoided.”

About the Author

Maureen Salamon, Executive Editor, Harvard Women's Health Watch

Maureen Salamon is executive editor of Harvard Women’s Health Watch. She began her career as a newspaper reporter and later covered health and medicine for a wide variety of websites, magazines, and hospitals. Her work has … See Full Bio View all posts by Maureen Salamon

About the Reviewer

Howard E. LeWine, MD, Chief Medical Editor, Harvard Health Publishing

Dr. Howard LeWine is a practicing internist at Brigham and Women’s Hospital in Boston, Chief Medical Editor at Harvard Health Publishing, and editor in chief of Harvard Men’s Health Watch. See Full Bio View all posts by Howard E. LeWine, MD

More than half of Americans live in states where recreational cannabis is legal. While alcohol remains the most-used drug in the US, daily cannabis use has actually outpaced daily drinking, according to a study following four decades of consumption trends. Changing drinking habits and new products likely play a role.

Are you rethinking drinking habits?

Growing interest in Dry January and the sober curious movement suggests many people — especially younger adults — are rethinking drinking habits. Sales of alcohol-free beverages have been on the rise. One popular new category in that mix is cannabis-infused beverages, says Dr. Staci Gruber, an associate professor of psychiatry at Harvard Medical School who directs the Marijuana Investigations for Neuroscientific Discovery (MIND) Program at McLean Hospital.

“People are interested in an experience that allows them to relax and enjoy themselves. Some are leaning into cannabis drinks as part of the ‘Cali sober’ trend,” says Dr. Gruber.

(Cali — or California — sober is an informal term used to describe people who abstain from alcohol, or just moderate their drinking, and avoid drugs other than cannabis. Some people include psychedelic drugs such psilocybin and LSD in their definition of Cali sober).

What are cannabis-infused drinks?

First, a brief primer on cannabis (marijuana). It comes from the Cannabis sativa plant, which contains more than 100 chemical compounds known as cannabinoids. These compounds interact with chemicals and receptors in the human brain.

• The most familiar cannabinoid is delta-9-tetrahydrocannabinol (THC), which produces intoxication or euphoria. For some people, it also helps ease pain and nausea.
• Another is cannabidiol (CBD), which is not intoxicating and has a number of potential medical uses, including anxiety-relieving properties.

Varieties of cannabis that contain low levels of THC (less than 0.3%) are classified as hemp, while those with more than 0.3% THC are considered cannabis. However, the type and amount of cannabinoids that different cannabis-based products claim to contain vary widely — and the labels aren’t necessarily accurate, says Dr. Gruber.

Many cannabis-infused drinks list THC as an ingredient, and while there is no standard dose, 5 milligrams (mg) is typically used in research studies of the drug. Some “low-dose” beverages contain 2 to 4 mg of THC in an 8-ounce container. Other products can contain as much as 200 mg of THC. The drinks may also contain caffeine, alcohol, or other substances.

State laws vary on whether and where these drinks can be sold and on age restrictions.

How do cannabis drinks differ from edibles?

Edibles are foods containing cannabis, such as gummies, brownies, or cookies.

The cannabinoids found in beverages are specially formulated to dissolve in liquid. This means they are more easily and rapidly absorbed into the body’s soft tissues.

“Some people say they feel the effects of cannabis-infused drinks within 15 to 20 minutes, which is much faster than when people eat a cannabis gummie or brownie,” says Dr. Gruber. Those products take at least 30 to 90 minutes to take effect because they must be digested and then processed through your liver, she explains.

How do the effects of cannabis drinks compare with alcoholic drinks?

While everyone is different, people generally know how they’re going to react if they drink, say, a light beer or two gin and tonics, says Dr. Gruber. But people are less familiar with the effects of cannabis in general — and of cannabis beverages in particular. That’s compounded by the varied amounts, mixtures, and other ingredients different drinks may contain.

If you down one cannabis drink and don’t wait long enough to feel the effects and have one or two more, you can double or triple your THC dose very quickly. “You can go from an experience that’s reasonably pleasant to one that’s not,” says Dr. Gruber.

Some people feel fine after small and sometimes even large amounts of THC. Others find even small amounts intolerable. “They may feel uneasy or anxious and their heart rate and blood pressure may rise. Nausea and vomiting are also possible, and some people even become paranoid and agitated,” says Dr. Gruber.

Are older adults more likely to experience unpleasant effects?

Possibly. Older adults may be more vulnerable to these unpleasant effects, in part because drug metabolism slows with age. After recreational cannabis became legal to sell in California, cannabis-related emergency department visits increased in older adults. The same trend occurred in Canada, as documented in a recent study in JAMA Internal Medicine.

This isn’t to suggest that cannabis drinks are more risky than alcohol, which has many unhealthy effects. Still, there are generally more unknowns with cannabis drinks, says Dr. Gruber.

“If you are interested in trying it and it is legal for you to do so, be mindful about controlling the experience until you know how a particular product affects you,” she says.

About the Author

Julie Corliss, Executive Editor, Harvard Heart Letter

Julie Corliss is the executive editor of the Harvard Heart Letter. Before working at Harvard, she was a medical writer and editor at HealthNews, a consumer newsletter affiliated with The New England Journal of Medicine. She … See Full Bio View all posts by Julie Corliss

About the Reviewer

Howard E. LeWine, MD, Chief Medical Editor, Harvard Health Publishing

Dr. Howard LeWine is a practicing internist at Brigham and Women’s Hospital in Boston, Chief Medical Editor at Harvard Health Publishing, and editor in chief of Harvard Men’s Health Watch. See Full Bio View all posts by Howard E. LeWine, MD