Health
Mosquito Repellents: Choosing the Best Repellant
Mosquitos don’t just whine in your ear and drive you mad with itching. They also spread disease to more than 700 million people every year. Here’s how to stay off a mosquito’s menu.
Do you seem to get eaten alive when others are left alone? You’re probably not just imagining it.
Everyone’s body chemistry is a little different, and some people are more likely to attract unwanted insect advances than others are.
Mosquitoes can sense your presence from far away. When you breathe out, you emit a plume of carbon dioxide that carries on the breeze, and CO2 also seeps from your skin.
Mosquitoes are attracted to carbon dioxide as well as the warmth and humidity you’re giving off, says Renee Anderson, PhD, a medical entomologist at Cornell University in Ithaca, NY. They follow the trail, flying in a zigzag pattern, until they find the source. In addition, they are also attracted to certain chemicals in your sweat. And mosquitoes love a moving target — it helps them zero in.
In general, mosquito repellent works by masking the chemical cues that welcome mosquitoes to dine.
DEET: Potent, But Safe
One of the most effective mosquito repellents is one of the oldest around. DEET was first developed for use by the U.S. Army in 1946, and it became available to the public in 1957. Many other products have hit the market since then, but few compare to DEET. In fact, it’s one of two ingredients in mosquito repellent that the CDC recommends for preventing mosquito-borne diseases. The other is picaridin, and the CDC believes these two ingredients are more effective than other mosquito repellents.
In a study published in the New England Journal of Medicine in 2002, researchers compared several types of mosquito repellents head-to-head in laboratory tests. Fifteen volunteers took turns sticking an arm treated with mosquito repellent into a cage full of mosquitoes. The researchers noted how long it took a mosquito to bite.
“OFF! Deep Woods” repellent, a product containing about 24% DEET, fared the best. Its protection lasted an average of 5 hours.
The least effective products were wristbands treated with DEET or citronella, which offered almost no protection. The researchers weren’t surprised. Mosquito repellent only works on the surface to which it’s applied directly. Mosquitoes are happy to bite skin only 4 centimeters away from the repellent slick.
DEET has an excellent safety record, despite some people’s concerns. N,N-diethyl-3-methylbenzamide doesn’t sound like something you’d want to spray on your skin, and perhaps its acronym reminds people of the dangerous and now banned insecticide DDT. But they’re nothing alike.
The Environmental Protection Agency must approve all pesticides used in the U.S., and although DEET isn’t a pesticide by definition — it does not kill insects — it falls under the EPA’s regulatory purview.
In 1998, the agency re-evaluated DEET and found that it is very safe when used according to label directions, and it’s not classified as a carcinogen (cancer-causing agent). The label directions on DEET products will say you should apply it only once a day to exposed skin and outerwear — not under clothing. Under clothes, it can absorb into the skin more readily, and possibly cause irritation. DEET can also irritate the eyes.
“The most common complaint is when DEET gets in the eyes, and obviously, that’s something to be avoided,” says Ed Tate, a spokesman for the Consumer Specialty Products Association, an industry group that funds the DEET Education Program.
Young children shouldn’t be allowed to apply DEET repellent themselves, but it is safe for them to use. The American Academy of Pediatrics (AAP) says products containing DEET are OK for children aged two months and older with a maximum DEET concentration in mosquito repellent for kids of no more than 30%. The AAP says insect repellents aren’t recommended for kids younger than 2 months.
Bite-Blocking Botanicals
Nevertheless, some still wish for an alternative mosquito repellent. At least since the 1970s, many have sworn by Avon’s Skin-So-Soft bath oil as an alternative.
“They believe there’s some magic in the bath oil,” says Andrew Pechko, a research and development manager at Avon. Of course, there isn’t.
The NEJM study shows that Skin-So-Soft worked as a mosquito repellent for an average of roughly 10 minutes, which hardly matched DEET products, or even soybean oil. In the study, a 2% soybean oil product called Bite Blocker for Kids protected against bites for an average of 94 minutes.
Avon does not market the original Skin-So-Soft oil as a mosquito repellent, but the company does have a formula containing IR3535, anEPA-approved mosquito repellent.
In the NEJM study, Bug Guard Plus protected against mosquito bites for only about 23 minutes, on average. But Avon has said that their “eXpedition” formula lasted as long as 8 hours in outdoor tests.
“The EPA, as a matter of fact, does not recognize a mosquito cage test to establish product labeling claims,” Pechko tells WebMD. “The EPA requires outdoor field studies.”
Besides all the sprays and lotions that contain mosquito repellent, there are many things that supposedly drive away mosquitoes in the surrounding area.
Citronella candles have been used since 1882 as a means of drawing mosquitoes away from people. But one study shows that they’re not much more effective than plain candles, which also give off heat, carbon dioxide, and moisture.
You may have seen ads for ultrasonic mosquito repellent devices, which supposedly emit sounds that irritate or scare away the bugs. Organizations including the Federal Trade Commission and the American College of Physicians (in a review in Annals of Internal Medicine) cite numerous studies showing that these devices don’t work.
There are also mosquito traps on the market. They emit carbon dioxide and a chemical called octenol. They’re supposed to lure mosquitoes away from people and into the trap.
“They do collect lots and lots of mosquitoes,” Anderson says. But it’s not clear if they really reduce the number of bites for people nearby.
The CDC has even created its own mosquito trap that uses hay and water in a bucket, with no insecticide or chemicals. These traps are called Autocidal Gravid Ovitraps.
As for the traditional electric bug zappers, don’t use them. The violet light may be irresistible to some flying insects, but mosquitoes largely ignore it. “It’s a lot of beneficial insects that are getting fried,” Anderson says.
The best way to keep swarms of mosquitoes from descending on your backyard barbecue is to get rid of standing water, where mosquitoes lay their eggs.
Some mosquito species lay eggs directly in stagnant water. Others lay eggs in containers — a tree hollow, birdbath, kiddie pool, tire swing, etc. — above the water line. Then, when it rains, the eggs are submerged and they hatch.
“You need to scrub out those containers,” Anderson says. “Simply dumping the water out isn’t going to dislodge those eggs that are attached along the side.”
May 10, 2024 – When we’re young, we take our macula for granted. At the center of our retina – the deepest layer of the eye that’s chock-full of photoreceptors and that confers color to our world – the macula is like a high-resolution camera. As light hits our eyes, the retina’s macula recasts our world in a bloom of color with astoundingly high visual sharpness.
But as you age, your vision dulls. What once stood out sharply becomes foggy, like condensation on a windowpane. After some time, a coal-black smudge or cloudy circular area begins to affect your central vision.
This effective blind spot widens over time if left untreated. What remains is a “macular hole” in the center of your retina.
This unfortunate series of events marks the advanced stage of age-related macular degeneration, a dangerous retinal disease that affects about 20 million people in the U.S., and nearly 200 million people worldwide.
And it’s not getting better. Estimates are that by 2040, the disease may affect nearly 300 million people worldwide. We are very limited in our ability to treat or prevent it. Read on for what to know.
First, What Causes Age-Related Macular Degeneration?
AMD’s causes are varied, and whether it will affect you is mostly determined by age and genetics, said Marco Alejandro Gonzalez, MD, an ophthalmologist and vitreoretinal specialist in Delray Beach, FL.
Because of the different cocktails that we have in terms of our genetic makeup, some people’s photoreceptor cells in the macula “basically start to shut down,” he said.
AMD’s development involves over 30 genes, and if you have a first-degree relative – parent, sibling, child – who has the disease, you’re three times more likely to get it, too.
Gonzalez explained how the expected rise to 300 million cases by 2040 is due mostly to improved diagnostic tools, along with the fact that the world is getting older and living longer. (Usually, an optometrist can detect signs of AMD during a routine eye exam.)
Eye experts still struggle to stop AMD’s most harmful sign – the cause of those muddy, milky, or even coal-colored circles in your central vision: geographic atrophy.
Geographic atrophy can occur in either of the two forms of age-related AMD: “dry” AMD and “wet” AMD.
Nearly every case of AMD begins as the dry kind, affecting 80% to 90% of AMD patients.
Retinal disease expert Tiarnán Keenan, MD, PhD, offered a vivid image of geographic atrophy for those who have dry AMD.
“As time passes, the circular patches of GA expand like a brushfire, taking more and more vision with it, often to the point of legal blindness,” he said.
A researcher in the Division of Epidemiology and Clinical Applications at the National Eye Institute, Keenan recently led a study that tested the efficacy of the antibiotic minocycline in slowing geographic atrophy expansion in dry AMD. The study operated on the grounds that the body’s immune system could be at play in developing the disease.
When your body’s immune system is overactive, microglial cells (central nervous system immune cells) can get into the sub-retinal space and possibly eat away at the macula and its sensitive photoreceptors.
Though minocycline had been shown to reduce inflammation and microglial activity in the eye in diabetic retinopathy, it didn’t slow the expansion of geographic atrophy or vision loss in patients with dry AMD during Keenan’s study.
When asked if microglial activity could have very little to do with the atrophy expansion, Keenan said it’s something to consider: “Maybe microglia are just there as bystanders clearing up the debris … so inhibiting them is less likely to slow down progression.”
In future drug trials, “maybe it’s possible the minocycline or another approach to target microglia would be helpful, but it would be needed in combination with some other therapy and be ineffective by itself,” he said.
Two Sides of the Same Disease
In dry AMD, Gonzalez compares macular degeneration to the loss of pixels on a screen. “Some of those pixels burn out … and that’s the way you lose vision classically in the dry form.”
Wet AMD is a more progressive form of the disease. It causes abrupt vision loss due to abnormal blood vessel growth.
“If you don’t treat wet AMD quickly, it’s game over,” warned Gonzalez. “Wet macular degeneration is the quicker process of vision loss because these blood vessels wreak havoc.” These new blood vessels bleed, causing fluid to build in the macula, which ultimately leads to scarring.
Gonzalez shed light on why wet AMD develops. “The wet form, for some reason, is the body’s last-ditch effort to try to kind of ‘help’ a dying macula. … When these blood vessels start to grow under the retina, they quickly destroy the architecture of the macula.”
Stopping the Bleeding in Wet AMD
Though wet AMD is rarer, it’s more treatable than dry AMD. Signs and symptoms can be eased with various therapies injected into the eye.
Putting it simply, Gonzalez said these therapies to treat wet AMD “all basically do the same thing. They make these new blood vessels regress temporarily before they cause damage to the macula.”
The injected medication clears away those blood vessels and restores the architecture of the macula. People can recover some vision in this way, but it’s only a temporary tune-up, and shots must be given as often as once a month.
“Degeneration of the cells is still the main problem. You’re not stopping that. But degeneration itself is a lot slower than actual vision loss associated with these blood vessels.”
The Struggle in Developing New Treatments
According to Keenan, “nobody has been able to stop geographic atrophy from happening” in either form of AMD. “So, that’s the main work in the field with trials.”
In December 2023, the FDA approved two new drugs: Syfovre and Izervay, both of which only slow geographic atrophy. Degeneration still happens, regardless.
Keenan explained how these two new drugs are “complement inhibitors … given by injection into the eye once a month or so.”
“Complement” refers to the body’s complement pathway, a trigger that activates a cascade of proteins in enhancing immune response.
Clinical trials showed Syfovre slowing the rate of geographic atrophy by up to 22% over 2 years, and Izervay up to 14% over 1 year.
Though these drugs are a new weapon against this troublesome affliction, they aren’t without their complications.
“Anytime you give an injection in the eye, there’s always the risk of an infection because you’re introducing something from the outside. So that’s the biggest risk,” explained Gonzalez.
An infection is uncommon, but potentially devastating, as you can lose your eye altogether. There’s also the chance of a damaging reaction to the shot.
“You have to pick and choose your patients,” said Gonzalez. “Not everybody is a good candidate for those new shots … and the patient is never going to see better. … It’s a harder sell than the ones for wet AMD.”
A Common Protective Measure
Keenan and Gonzalez both have a fair degree of confidence in reducing the risk of AMD with vitamin therapy.
As a bit of background on how vitamins were found to act as a sort of preventive measure, Gonzalez said, “In the early and late ‘90s, there were series of studies which were called the age-related eye disease studies.” These are now referred to as AREDS 1 and AREDS 2.
Researchers proved that a certain cocktail of vitamins slowed down degeneration. The most is a combo of antioxidants: vitamins C and E and lutein and zeaxanthin, all of which are in the AREDS 2 formula.
People who took these vitamins had a lower chance of losing their vision over the next 2 to 5 years. “[The combo] seems to be complementary and additive … with a combined treatment effect of 55% to 60%, an excellent safety record, and very low cost,” Keenan said.
Gonzalez recommends the AREDS 2 formula of vitamins to every patient of his. “It’s such an easy thing to take, and the downside is minimal.”
Unfortunately, if your genes make you more likely to have the condition, a change in diet or vitamin use could have no effect.
Dire? Possibly. But not all is lost in this fight.
Vigilance with AMD and What to Do Next if You’re Diagnosed
Gonzalez is adamant in educating his patients before time has run out on treating AMD. Recognition is key. “The most common reason a lot of these people get to me ‘too late’ is they don’t realize there’s a problem.”
He explained a typical scenario: “Let’s say you have macular degeneration in both eyes at different stages. One of your eyes starts developing wet macular degeneration … so the better eye takes over and you may not notice there’s a problem.”
Even after a patient is diagnosed with AMD, they usually see a specialist only twice a year. Gonzalez often tells his patients to cover one of their eyes to make sure their vision is intact in both eyes. “You’ll be able to pick up on subtle differences” in each eye, he said.
This type of self-care and vigilance can be the difference between successfully living with and treating the disease for the rest of your life, and trying to get help when it’s simply too late.
For wet AMD, as mentioned before, a round of injections is basically what everyone does. Without quick, invasive treatment, the point of no return approaches rapidly.
May 16, 2024 – Multiple U.S. agencies are working to contain the recent bird flu outbreak among cattle to prevent further spread to humans (beyond one case reported in early April) and use what we learned before, during, and after the COVID-19 pandemic to keep farm workers and the general public safe.
Fingers crossed, the bird flu will be contained and peter out. Or the outbreak could continue to spread among dairy cattle and other animals, threatening the health and livelihoods of farmers and others who work with livestock.
Or the virus could change in a way that makes it easier to infect and spread among people. If this happens, the worst-case scenario could be a new influenza pandemic.
With so many unknowns, WebMD brought together experts from four federal agencies to talk prevention, monitoring, and what the “what ifs” of bird flu might look like.
Communication with the public “about what we know, what we don’t know, and ways you and your family can stay safe is a priority for us at CDC,” said Nirav D. Shah, MD, JD, the CDC’s principal deputy director. “We at the federal level are responding, and we want the public to be following along.”
People should consult the websites for the CDC, FDA, U.S. Department of Agriculture (USDA), and the Administration for Strategic Preparedness and Response (ASPR) for updates.
It is essential to not only stay informed, but to seek trusted sources of information, Shah said during “Bird Flu 2024 – What You Need to Know,” an online briefing jointly sponsored by the CDC and WebMD.
An ‘Experimental Hamburger’
If one take-home message emerged from the event, it was that the threat to the general public remains low.
The retail milk supply is safe, although consuming raw or unpasteurized milk is not recommended. “While commercial milk supply is safe, we strongly advise against drinking raw milk,” said Donald A. Prater, DVM, acting director for the FDA’s Center for Food Safety and Applied Nutrition.
As for other foods, thoroughly cooked eggs are less risky than raw eggs, and the nation’s beef supply remains free of the virus as well.
For years, federal inspectors have purchased and tested meat at retail stores, said Eric Deeble, DVM, USDA deputy assistant secretary for the Office of Congressional Relations. So far, H5N1, the virus behind bird flu, has not been detected in beef.
The USDA took testing a step further and recently cooked ground beef from dairy cows in their lab. Using what Deeble described as an “experimental hamburger,” the agency showed cooking beef to 165 F or higher kills the virus if it ever becomes necessary.
The federal government now requires all cattle be tested and be free of bird flu virus before crossing any state lines. The government is also reimbursing farmers for veterinary care and loss of business related to the outbreak, and supply personal protective equipment (PPE) like gloves, masks, and face shields to workers.
Vaccination Not Recommended Now
Federal scientists know enough about H5N1 virus to create vaccines against it quickly if the need arises. It’s more about planning ahead at this point. “Vaccines are not part of our response right now,” said David Boucher, PhD, director of infectious diseases preparedness and response at the Administration for Strategic Preparedness and Response.
If the virus changes and becomes a bigger threat to people, “we have the building blocks to produce a vaccine,” Boucher added.
An event attendee asked if the seasonal flu shot offers any protection. “Unfortunately, the flu shot you got last year does not provide great protection from the avian flu,” Shah responded. “It might do a little bit … but that is the vaccine for seasonal flu. This is something more novel.”
Treatments Stockpiled and Ready
Antiviral medications, which if given early in the course of bird flu infection could shorten the severity or duration of illness, are available now, Shah said. The dairy farmer who was infected with bird flu earlier this year responded to oseltamivir (Tamiflu) treatment, for example.
When it comes to bird flu symptoms, the fact that the only infected person reported so far this year developed pink eye, also known as conjunctivitis, is interesting, Shah said. Officials would have expected to see more typical seasonal flu symptoms, he added.
“Influenza is not a new virus,” Boucher said. “With this strain of influenza, we are not seeing any genetic markers associated with resistance to antivirals. That means the antivirals we take for seasonal influenza would also be available if needed to treat H5N1.”
ASPR has stockpiled Tamiflu and three other antivirals. “We do have tens of millions of courses that can be distributed around the country if we need them,” he added.
“Influenza is an enemy we know well,” Boucher said. That is why “we have antivirals ready to go now and many types of PPE.”
Science in Action
The feds intend to stay on the case. They will continue to monitor emergency department visits, lab test orders, and wastewater samples for any changes suggesting a human pandemic risk is growing.
“While we’ve learned a great deal, there are still many things we do not know,” Deeble said.
Shah added, “As in any outbreak, this is an evolving situation and things can change. What you are seeing now is science in action.”
For the latest updates on bird flu in the United States, visit the CDC’s H5N1 Bird Flu: Current Situation Summary website.
May 16, 2024 – Multiple U.S. agencies are working to contain the recent bird flu outbreak among cattle to prevent further spread to humans (beyond one case reported in early April) and use what we learned before, during, and after the COVID-19 pandemic to keep farm workers and the general public safe.
Fingers crossed, the bird flu will be contained and peter out. Or the outbreak could continue to spread among dairy cattle and other animals, threatening the health and livelihoods of farmers and others who work with livestock.
Or the virus could change in a way that makes it easier to infect and spread among people. If this happens, the worst-case scenario could be a new influenza pandemic.
With so many unknowns, WebMD brought together experts from four federal agencies to talk prevention, monitoring, and what the “what ifs” of bird flu might look like.
Communication with the public “about what we know, what we don’t know, and ways you and your family can stay safe is a priority for us at CDC,” said Nirav D. Shah, MD, JD, the CDC’s principal deputy director. “We at the federal level are responding, and we want the public to be following along.”
People should consult the websites for the CDC, FDA, U.S. Department of Agriculture (USDA), and the Administration for Strategic Preparedness and Response (ASPR) for updates.
It is essential to not only stay informed, but to seek trusted sources of information, Shah said during “Bird Flu 2024 – What You Need to Know,” an online briefing jointly sponsored by the CDC and WebMD.
An ‘Experimental Hamburger’
If one take-home message emerged from the event, it was that the threat to the general public remains low.
The retail milk supply is safe, although consuming raw or unpasteurized milk is not recommended. “While commercial milk supply is safe, we strongly advise against drinking raw milk,” said Donald A. Prater, DVM, acting director for the FDA’s Center for Food Safety and Applied Nutrition.
As for other foods, thoroughly cooked eggs are less risky than raw eggs, and the nation’s beef supply remains free of the virus as well.
For years, federal inspectors have purchased and tested meat at retail stores, said Eric Deeble, DVM, USDA deputy assistant secretary for the Office of Congressional Relations. So far, H5N1, the virus behind bird flu, has not been detected in beef.
The USDA took testing a step further and recently cooked ground beef from dairy cows in their lab. Using what Deeble described as an “experimental hamburger,” the agency showed cooking beef to 165 F or higher kills the virus if it ever becomes necessary.
The federal government now requires all cattle be tested and be free of bird flu virus before crossing any state lines. The government is also reimbursing farmers for veterinary care and loss of business related to the outbreak, and supply personal protective equipment (PPE) like gloves, masks, and face shields to workers.
Vaccination Not Recommended Now
Federal scientists know enough about H5N1 virus to create vaccines against it quickly if the need arises. It’s more about planning ahead at this point. “Vaccines are not part of our response right now,” said David Boucher, PhD, director of infectious diseases preparedness and response at the Administration for Strategic Preparedness and Response.
If the virus changes and becomes a bigger threat to people, “we have the building blocks to produce a vaccine,” Boucher added.
An event attendee asked if the seasonal flu shot offers any protection. “Unfortunately, the flu shot you got last year does not provide great protection from the avian flu,” Shah responded. “It might do a little bit … but that is the vaccine for seasonal flu. This is something more novel.”
Treatments Stockpiled and Ready
Antiviral medications, which if given early in the course of bird flu infection could shorten the severity or duration of illness, are available now, Shah said. The dairy farmer who was infected with bird flu earlier this year responded to oseltamivir (Tamiflu) treatment, for example.
When it comes to bird flu symptoms, the fact that the only infected person reported so far this year developed pink eye, also known as conjunctivitis, is interesting, Shah said. Officials would have expected to see more typical seasonal flu symptoms, he added.
“Influenza is not a new virus,” Boucher said. “With this strain of influenza, we are not seeing any genetic markers associated with resistance to antivirals. That means the antivirals we take for seasonal influenza would also be available if needed to treat H5N1.”
ASPR has stockpiled Tamiflu and three other antivirals. “We do have tens of millions of courses that can be distributed around the country if we need them,” he added.
“Influenza is an enemy we know well,” Boucher said. That is why “we have antivirals ready to go now and many types of PPE.”
Science in Action
The feds intend to stay on the case. They will continue to monitor emergency department visits, lab test orders, and wastewater samples for any changes suggesting a human pandemic risk is growing.
“While we’ve learned a great deal, there are still many things we do not know,” Deeble said.
Shah added, “As in any outbreak, this is an evolving situation and things can change. What you are seeing now is science in action.”
For the latest updates on bird flu in the United States, visit the CDC’s H5N1 Bird Flu: Current Situation Summary website.
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