Oh, the perils of vacationing in mosquito territory. These little bloodsuckers have made a meal of me around the globe, and I’ve longed for a definitive guide to repelling them. What really works? When and where are extra precautions necessary?  I turned to scientists who study mosquito behavior to find out. They took a break from investigating neurons and odor receptors to offer travel advice, including whether to spend money on botanical repellents and why it might be wise to forgo that glass of wine.  Repelling mosquitoes isn’t just a matter of avoiding unsightly, itchy bumps. Mosquitoes spread some of the world’s most deadly diseases. Malaria alone kills about a million people a year, according to the World Health Organization.  “Mosquitoes are able to seek out a human being like a guided missile,” said Anandasankar Ray, a scientist at the University of California, Riverside.  It helps to know your enemy in order to conquer her (yes, her — only female mosquitoes bite). To that end, let’s briefly consider the situation from the mosquito’s point of view.  As it turns out, you play a part in her raison d’être. She bites you, explained Dr. Ray, because she requires material from your blood to produce her eggs. Imagine a mosquito flitting about when suddenly she encounters a little cloud of carbon dioxide. This plume is one of many coming out of your mouth as you lounge poolside in Rio with a caipirinha. Special sensors allow the mosquito to detect the plume, a sign that a living vertebrate is near.  As she draws close to the source, her sensors pick up odors emitted from your skin. These odors, many of which are produced by bacteria in your skin, help the mosquito determine that you’re not a horse or a dog but a human — her favorite meal. She homes in on you, possibly aided by infrared radiation coming off your warm body.  “Almost like in the ‘Predator’ movies,” Dr. Ray said.  Then — zap! — she pierces the nape of your neck, extracting the drops of blood necessary for the creation of her progeny.  But back to you and your needs.  TAKING COVER To protect yourself, you must know where and when the mosquitoes that carry debilitating diseases — malaria, filariasis, yellow fever, dengue — bite.  “If you’re in Central America, South America, Southeast Asia, Vietnam, Thailand, Malaysia — all of these places that are the most beautiful travel destinations, it’s really a concern,” said Leslie B. Vosshall, a scientist at Rockefeller University in New York who works with flies, mosquitoes and humans to study how odor is processed and perceived.  Dengue and yellow fever are primarily spread by Aedes aegypti, mosquitoes that live in tropical and subtropical areas — though they are increasingly found in urban areas — including Africa, Asia, North America, the Caribbean and Latin America (pay attention, World Cup travelers). This species bites during the day. Feeding typically spikes a couple of hours after sunrise and late afternoon, said Dr. Ray, whose findings about mosquito receptors, published last year in the journal Cell, could eventually help control disease transmission.  Each year about 50 to 100 million people get dengue fever, a viral infection that often requires hospitalization and can develop into deadly hemorrhagic fever, according to the W.H.O. There is no vaccine and no cure. Bed nets, said Dr. Ray, are a must.  Aedes aegypti can also transmit the chikungunya virus, which causes fever and joint pain. Chikungunya has hit Asia, Africa, India, Europe and the Americas (and into the eastern Caribbean this winter), according to the W.H.O. While there is no cure, most patients recover, though joint pain can persist for months or years.  Another species, Culex, may carry lymphatic filariasis, an infection that can result in elephantiasis. Places most at risk include Bangladesh, Democratic Republic of Congo, Ethiopia, India, Indonesia, Myanmar, Nigeria, Nepal, Philippines and the United Republic of Tanzania. Culex mosquitoes can also carry West Nile virus, found in Africa, Europe, the Middle East, North America and West Asia. These mosquitoes prefer birds but will bite humans, too. In the evening you may see them on the walls of your hotel room.  “They will try and descend on you while sleeping,” Dr. Ray said. Use a bed net.  Anopheles gambiae, mosquitoes that can spread malaria, often bite at dusk and late at night, Dr. Ray said. The W.H.O. says travelers are at risk of malaria infection in 99 countries, mostly in Africa, Asia and the Americas. Yet unlike dengue and chikungunya, malaria can be prevented, even treated, with medication.  WHAT WORKS, WHAT DOESN’T “The gold standard of insect repellency continues to be DEET,” Dr. Ray said. Developed by the Army in 1946, DEET is a chemical that can melt your nail polish. That said, the Environmental Protection Agency does not consider it to be a health concern if it is used infrequently and properly. (The agency’s DEET toxicity study is at epa.gov/oppsrrd1/REDs/factsheets/0002fact.pdf.)  “There’s no question that it’s the most effective skin repellent on earth,” Dr. Vosshall said.  DEET is sold in concentrations from less than 5 percent to 100 percent. Wearing long sleeves and pants will reduce the amount you need to use. Still, covering up (even in clothing with built-in repellent) is not foolproof. “If they’re very desperate,” Dr. Vosshall said, mosquitoes will “bite through jeans.”  An alternative is Avon Skin So Soft with picaridin, a synthetic version of piperine, the active component of black pepper. (Unlike DEET, it won’t dissolve plastics.)  What about natural botanical repellents that rely on plant extracts?  “It smells better and it doesn’t melt your sunglasses,” Dr. Vosshall said. But “the scientific evidence that those things work is weak to nonexistent.”  Some travelers swear by slapping on a vitamin B patch or eating garlic.  “It’s probably going to repel your friends but it really wouldn’t have an effect on mosquitoes,” Dr. Ray said.  Yet certain unconventional techniques can help, like taking showers (mosquitoes are drawn to sweat that has been on your skin for a while, Dr. Ray said) and, for reasons that remain unclear, avoiding alcohol.  “When people drink alcohol they become attractive to mosquitoes,” he said. (And you thought that only worked on other humans.)  There are also spatial repellents, which you should buy if you are vacationing in a country with mosquito-borne diseases and your accommodations do not have window screens. The safest of these repellents release a low amount of insecticide, like ThermaCELL lanterns, which use butane cartridges to heat mats saturated with repellent that then rises into the air. The effect of long-term exposure, however, is not clear. The OFF! clip-on mosquito repellent battery-powered fan also circulates repellent (the active ingredient is metofluthrin, which is a neurotoxicant). This will work if, for example, you’re camping and clip it inside your tent, said Dr. Ray, but not necessarily outdoors on a breezy day.  Citronella candles and oils “work somewhat,” he said. So does having someone around whom mosquitoes find irresistible.  “Many different groups have tested this idea that some people are more attractive than others and it’s absolutely true,” Dr. Vosshall said. “But we don’t exactly know why.”  IN THE FUTURE DEET has been the go-to solution for more than 70 years, but that’s changing. Last year, Dr. Ray and his colleagues revealed that they had discovered possible chemical substitutes for DEET that also have a milder smell, like that of grapes or sandalwood. Such findings will likely “lead to brand new, safer and more pleasant and perhaps more affordable mosquito repellents over the next two years,” he said. “And hopefully in four or five years we’ll find a DEET substitute that wouldn’t need to be spread all over your skin and could perhaps be used as a perfume or an after-shave.”  Eau de Aedes aegypti? Here’s hoping.  A version of this article appears in print on April 6, 2014, on page TR2 of the New York edition with the headline: Getting the Jump on a Tiny Foe. Order Reprints|Today's Paper|Subscribe
Arm yourself with information about risks and prevention techniques to gain an advantage in the battle against bites.