Mosquitoes are more than just pests. Despite their tiny size, they are one of the deadliest creatures on the planet, spreading diseases that kill millions of people each year worldwide, according to the World Health Organization. 

With mosquito season upon us—when temps start to hit 50°F and higher, depending on where you live—it’s time to amp up your awareness and protection efforts at home and on ­vacation. Bottom Line Personal spoke to Phyllis Kozarsky, MD, an ­infectious disease and travel medicine doctor about which diseases to worry most about, the best ways to ward off ­mosquitoes and how to keep your worries in perspective. 

How Worried Should You Be?

Unless you live in or travel to an area where mosquitoes are common, you don’t need to be terribly worried. Still, it’s worth protecting yourself because mosquito bites are plenty uncomfortable and they can lead to complications such as infection and allergic reactions. Other common worries about mosquitoes…

Using chemical insect repellents. If you’re in an area where any type of mosquito-borne illness can be transmitted, the risk for the illness usually is far greater than any risk from applying a chemical such as DEET to your skin. The only real documented risk when DEET is used as directed is rash, redness and swelling that can occur if you leave it on for extended periods of time. Stick to repellents that contain 20% to 25% DEET…apply it only when necessary…and wash it off as soon as you come inside. Repellents that contain picaridin, a less toxic option than DEET, are equally effective, don’t have the same greasy feel and don’t damage synthetic materials. 

Household pets. Mosquitoes bite furry friends, too, so definitely take precautions in warm, humid weather, such as avoiding long walks at dawn and dusk and eliminating standing water on your property. Talk to your veterinarian about an appropriate pet-friendly repellent and heartworm-prevention treatment—an infected mosquito can transmit heartworm as well.

Spraying your yard. While these monthly treatments are pretty effective at killing off mosquitoes, especially in low-lying and swampy areas, they do contain chemicals that you may not want your young children, grandchildren and pets rolling around in. If you’re a vegetable gardener, you also may have to avoid eating what you grow for a time after spraying occurs.

Going for a hike or swimming in a lake. Your risk from either of these activities depends on the time of day. Avoid both in the evening hours to be safest, and apply an effective repellent if you can’t. Exception: If you’re in an area where Zika, dengue, chikungunya or yellow fever is transmitted (see below), you’ll need to be vigilant about protection during the day, too.

Most Dangerous Mosquito-Borne Illnesses

There are many mosquito-borne ­illnesses worldwide and likely new ones will emerge. Two of the biggest are outside of the US—Japanese encephalitis (in Asia and the Western Pacific) and yellow fever (in South America and ­Africa). The following five are in the US, and only malaria has medication to treat it. The others are treated with medications for symptom relief. Symptoms will usually abate after treatment, but some will have lingering effects even after treatment. Pay attention to local health alerts regarding the types of mosquitoes in your area.

Chikungunya. The Aedes aegypti and Aedes albopictus species of mosquito transmit chikungunya and bite during the day and night. 

Where you can get it: North and South America, Africa, Asia and islands in the Caribbean, Indian Ocean and Western and South Pacific.

Symptoms: Abrupt onset of fever frequently accompanied by debilitating joint pain, muscle pain, joint swelling, headache, nausea, fatigue and rash.

Chikungunya can leave someone with an uncomfortable lingering arthritis. 

Dengue. This tropical mosquito-borne illness usually isn’t deadly, but it can make you seriously sick. Dengue is also spread by Aedes aegypti and Aedes albopictus mosquitoes that bite in the daytime and at night.

Where you can get it: The Caribbean, North and South America, western ­Pacific islands, Australia, Southeast Asia and Africa. Although not common in the US, outbreaks have occurred occasionally in Florida and California.

Symptoms: Fever, headache, nausea, vomiting, rash and pain in the eyes, joints and muscles. Symptoms can take up to two weeks to develop but typically last less than a week. More severe symptoms that require immediate medical attention include stomach pain and tenderness, vomiting and/or vomiting blood, bleeding from the nose or gums, blood in the stool and feeling tired, restless or irritable.

Malaria. This life-threatening illness is caused by a parasite that is released into your bloodstream when an infected mosquito bites you. The Anopheles mosquito that transmits malaria is most likely to bite just before dawn and right after darkness sets.

Where you can get it: Southern parts of North America, South America, the Caribbean, Africa, Asia, parts of Europe, the Middle East and the South Pacific.

Symptoms: High fever, shaking, chills and flulike illness. Symptoms usually appear between seven and 30 days after you’ve been bitten but can occur up to a year later.

Treatment: If you’re traveling to an area where malaria is endemic, you’ll need to take prescription medication before, during and after your trip. See a knowledgeable travel medicine expert—you can find one near you at the website of the International Society of Travel Medicine (ISTM.org). The type of medication you’ll be given depends on your specific health issues and other medications you may be taking.

West Nile Virus. The leading cause of mosquito-borne disease in the continental US, West Nile Virus most often causes no symptoms at all but in rare cases can lead to neurological symptoms and even death. The Culex mosquito carries West Nile and typically feeds from evening until morning.

Where you can get it: North America, Africa, Europe, the Middle East and west and central Asia.

Symptoms: Eight out of 10 people have no symptoms. One in five may develop fever, headache, tiredness, nausea, vomiting, swollen lymph glands and rash. About one in 150 people develop serious symptoms, including high ­fever, neck stiffness, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis.

Zika Virus. This virus is primarily a risk for pregnant women, those considering pregnancy and their partners because it can cause serious birth defects. People in these categories should not travel to areas where Zika can occur. Most people, however, don’t get sick or have only mild symptoms. The same mosquitoes that carry chikungunya and dengue transmit Zika, biting both day and night. 

Where you can get it: The Caribbean, Central and South America, Southeast Asia. In the US, there have been cases in more than a dozen states in the last few years. 

Symptoms: Fever, rash, headache, joint and muscle pain, conjunctivitis, lasting a few days to a week. 

5 Natural Ways to Repel Mosquitoes

Here are some nonchemical ways that you can ward off these bloodsuckers… 

Fragrance-free products. Mosquitoes may be attracted to scent, so use as many fragrance-free products as possible including personal-care products such as lotions and soaps, laundry detergents and fabric softeners and cleaning products. Don’t wear perfumes or cologne.

Shower after exercising (with unscented soap). Mosquitoes are attracted to damp, sweaty skin as well as to the carbon dioxide and lactic acid that our bodies secrete when we are active.

Turn on an outdoor fan. Mosquitoes are notoriously bad fliers and will avoid breezy areas.

Dress to protect. In addition to wearing as much clothing as you can tolerate in the heat, choose light-­colored fabrics—particularly beiges and whites—because mosquitoes prefer dark colors. 

Wear sneakers and socks instead of sandals—mosquitoes love dirty, sweaty feet.