They’re the uninvited guests you can always count on to ruin your backyard barbecue, summer vacation, or campout: Bugs that bite and sting — making any time spent in the great outdoors …well, a little less great.

Insect repellents are your best defense against those pesky pests, but a new analysis by Consumer Reports finds some bug sprays don’t offer much protection and may even contain potentially harmful ingredients.

The good news: The more effective insect repellents rated by Consumer Reports were also among the safer choices. In fact, the two top-rated products — Sawyers Fisherman’s Formula and Repel Lemon Eucalyptus — outperformed products that contained up to 25 percent DEET, a chemical that can cause serious side effects.

The active ingredient in Sawyer Fisherman’s Formula is 20 percent picaridin, and for Repel Lemon Eucalyptus it’s 30 percent oil of lemon eucalyptus. Both products were able to keep mosquitoes and deer ticks away for at least seven hours, the analysis showed.

“They are not side-effect-free, but those problems are less severe than DEET,” said Ellen Kunes, Consumer Reports’ heath and food content development team leader. “Still, all repellents should be used sparingly and only for the time you need them — especially on children and older people.”

Biting and stinging insects are more than just a nuisance; some carry serious infections and diseases.

• Mosquitoes spread a range of blood-borne disease, including encephalitis, Chikungunya, and West Nile virus, which be serious or deadly for older people and those with compromised immune systems.
• Tick bites can lead to Lyme disease, caused by the bacterium Borrelia burgdorferi, spread by the black-legged deer tick — about the size of the period at the end of this sentence. Ticks can also cause other diseases, such as Rocky Mountain spotted fever.
• Stings and bites from bees, hornets, spiders, and other insects can cause life-threatening allergic reactions in some people or become infected.

To identify the safest and most effective spray-on repellents, Consumer Reports hired an outside laboratory to test 15 pump sprays and aerosols repellents. The products contained DEET, picaridin, oil of lemon eucalyptus, a chemical called IR3535, and products made with natural plant oils.

Testers applied repellents to their forearms and reached small cages containing 200 female mosquitoes. Experts recorded bites every hour and ranked the products, accordingly.

Top-rated repellents:

• Sawyers Fisherman’s Formula.
• Repel Lemon Eucalyptus
• Repel Scented Family (which contains 15 percent DEET).
• Off! Deepwoods (25 percent DEET).
• Natrapel 8 Hour.
• Coleman SkinSmart

Lowest-rated products:

• EcoSmart Organic.
• Off! Family Care II Clean Feel.
• California Natural Baby Bug Blend.
• All Terrain Kids Herbal Armor.
• BullFrog Mosquito Coast
• Babyganics Natural.
• Burt’s Bees Herbal.
• Cutter Natural.
• Cutter Skin Sensations.

Consumer Reports tests also found that products with natural plant oils — such as citronella, lemongrass, and rosemary — did not always live up to their manufacturers’ claims they are “proven effective” against mosquitoes or “repels mosquitoes for hours.” In addition, two products — Babyganics Natural and EcoSmart Organic — imply that they’re organic. But neither contains certified organic ingredients, as per U.S. Department of Agriculture provisions.

But Consumer Reports experts noted two natural alternatives to DEET — picaridin and oil of lemon eucalyptus — did well in the tests. Both have less serious side effects than DEET, but care should still be taken whenapplying such products on kids.

1. When using bug repellents, experts recommend the following precautions:
2. Apply them only to exposed skin or clothing (as directed on the product label). Never put it on under clothing. Don’t apply over cuts, wounds, or irritated skin.
3. When applying to the face, spray first on your hands, then rub in, avoiding the eyes and mouth.
4. Don’t use near food and wash hands after application and before eating or drinking.
5. Health experts also advise seeking immediate medical attention if a bug bite or sting produces any of the following symptoms: Difficulty breathing; feeling your throat is closing; swelling of lips, tongue, or face; chest pain, a racing heartbeat for more than a few minutes; dizziness or headache; vomiting.
6. Contact a Poison Control Center (1-800-222-1222) if you or your child experience a reaction to insect repellent.