If you need a repellent, first try a plant-based product. (iStockphoto)

Summer bugs can do more than ruin your summer fun: Mosquitoes can transmit West Nile virus, and ticks can carry Lyme disease, among other problems. Those diseases can cause debilitating aches and pains and, in rare cases, death. This year, add a new worry: chikungunya. The mosquito-borne disease, which can cause crippling arthritis, is now in the Caribbean, and experts worry that it may arrive on the U.S. mainland soon.

Consumer Reports’ tests have found that some insect repellents, especially those with the chemical DEET, can help keep bugs away. But its safety experts say that the products may also pose risks. “We think that DEET and other chemical-based repellents should be used only if other, safer methods don’t work for you,” says Urvashi Rangan, director of Consumer Reports’ Food Safety and Sustainability Center.

Here’s what you need to know about insect-borne disease, safe ways of avoiding insects and, when necessary, how to use repellents safely.

Dangerous bugs

Some 300,000 people each year are infected with Lyme disease, which can cause fever, muscle and joint pain, and other flulike symptoms. Antibiotics can cure Lyme, but if it’s not treated, it can cause numbness, facial paralysis and serious heart problems.

West Nile is less common but riskier: In 2012, the deadliest year on record, there were 5,674 reported cases, including 286 deaths. It’s a viral infection, so antibiotics don’t help. Instead, doctors ease symptoms with over-the-counter pain relievers and, in severe cases, intravenous fluids and prescription pain drugs.

Dealing with DEET

DEET (N,N-diethyl-meta-toluamide), first used by the U.S. Army, has been sold to consumers since the 1950s. It can cause allergic skin reactions, particularly at concentrations of 50 percent and above, and eye irritation. A 2013 analysis of about 4,000 DEET-related calls to poison control centers found that 450 people needed medical treatment after applying DEET; two died. Most cases of seizures, slurred speech, coma and other serious side effects have occurred in people who ingested DEET or applied it for three or more days in a row, or used products with 95 percent DEET or more.

It’s unclear whether lower doses pose the same risks, especially if you follow directions. Still, our experts urge children, seniors and those with weakened immunity to use it with extra caution. The American Academy of Pediatrics says DEET shouldn’t be used on infants younger than 2 months, and Canada’s federal health department says children 6 months to 12 years old should avoid products with more than 10 percent DEET.

“Most important, people should first try safer ways of avoiding bugs,” Rangan says. She points out that in our tests, products with 30 percent or less DEET worked well. “So if you decide you really want to try DEET, stick with the lowest effective dose, and avoid those that are more than 30 percent DEET.”

Smartest precautions

●Avoid tight clothes (which mosquitoes can penetrate), dark clothes (where ticks can hide) and strong scents (which attract mosquitoes).

●Stay inside as much as possible when mosquitoes are out: sunrise, sunset and early evening.

●When you’re sitting on a deck or patio, plug in a fan to blow away mosquitoes.

●When heading out to woody or grassy areas, tuck pants into socks, wear boots and tuck hair into a hat. When you get home, check for ticks, shower and toss clothes into a dryer.

●If you need a repellent, first try plant-based products. If you opt for DEET, use products with low concentrations, such as Off Family-Care Smooth & Dry spray (15 percent).

●Apply repellents outdoors and use them only on clothing or exposed skin (not under clothes), and wash clothes before wearing them again.

Copyright 2014. Consumers Union of United States Inc.

For further guidance, go to www.ConsumerReports.org/Health, where more detailed information, including CR’s ratings of prescription drugs, treatments, hospitals and healthy-living products, is available to subscribers.