Bugs not only ruin summer barbecues, but they also transmit serious illnesses like Lyme disease and West Nile virus. "There are few places where the insect-disease risk is zero, and hot spots change," says Emily Zielinski-Gutierrez of the Centers for Disease Control and Prevention (CDC). The best everyday defense against bugs is DEET, a chemical that deters insects by interfering with their ability to land. DEET comes in concentrations from 4 percent to 100 percent.

RELATED: Four Dangerous Diseases that Mosquitoes Are Bringing to the U.S. 

The greater the number, the longer it lasts — but don’t use higher than necessary concentrations or larger than needed amounts, as some studies suggest that too much may cause adverse health and ecological effects. Finally, DEET isn’t the only game in town: In some situations, other ingredients work just as well, if not better, provided you know what to look for. 

Best for Exercising: Off! Active
When you’re running, riding, or playing outdoors, look for a sweat-resistant repellent made from DEET or picaridin, a chemical used worldwide since 1998 but only recently approved in the U.S. Choose a spray with 15 percent DEET or 15 percent picaridin like Off! Active ($7) or Repel Sportsmen Gear Smart ($6) to keep bugs away for at least two hours of exercise; reapply if outside longer.

Best for Not Smelling up the Party: Natrapel 8 Hour
Avoid the bug-spray smell of DEET with a repellent that uses picaridin, a scentless chemical that prevents bugs from finding human targets. Studies show that picaridin is less irritating to skin than DEET and won’t damage fabrics and plastics like the latter can. Picaridin concentrations over 7 percent were just recently introduced in the U.S.; scout out Natrapel 8 Hour ($6) with 20 percent picaridin.

Best for preTreating Fabric: Sawyer Permethrin Clothing & Gear
Before camping or hiking in tick-­infested regions — whether for one night or 10 days — treat tents, packs, and clothing with permethrin, an insecticide that kills bugs on contact. Spray a product such as Sawyer ($16) on your clothing or gear, allow to dry, and you’re protected for six weeks. Permethrin should come out of clothing after six cycles in the washer.

Best for Going Natural: Repel Lemon Eucalyptus Spray
When you’re not in grass or trees where ticks live, choose a natural repellent made from lemon eucalyptus oil, which can buck mosquitoes for several hours but won’t deter ticks. Lemon eucalyptus is the only natural repellent approved by the CDC and is less irritating to the skin than DEET, picaridin, or permethrin. A product like Repel ($6) can last up to six hours.