How Insect Repellents Work and What to Look For Before Buying

Bernard Lee, PharmD — Sat, 06 Feb 2010 06:00:00 GMT

1. How do repellents work?

Mosquitoes are attracted to moisture, carbon dioxide, warmth, odor, and estrogen on skin. Insect repellents work by producing a vapor layer that has an unpleasant taste or smell to insects.

2. Why should insect repellents be used?

Mosquitoes can transmit fatal diseases worldwide (i.e. West Nile virus, malaria and yellow fever).

3. When should insect repellents be used?

Anytime you or your child are going to be outside. In many areas of the country, mosquitos not only bite at night, but also during the day.

4. Who should use insect repellents, or take precautions against insects?

Anyone who is at risk for exposure to insects (i.e. mosquito bites) that may cause local skin or allergic reactions. If you or your child is exposed to insects that can cause serious illness or death by spreading bacteria or viruses (such as the West Nile virus).

5. Who should NOT use insect repellents?

-Anyone who has a history of a skin irritation or an allergic reaction to insect repellents should not use repellents with known ingredients (active or inactive) that caused these reactions. Read the labels carefully to find out what ingredients are in a product.

-The American Academy of Pediatrics (AAP) generally recommends that infants under 2 months old should not use insect repellents containing N,N-Diethyl-meta-toluamide (DEET).

6. What makes a product an ideal insect repellent?

•   Long lasting or works long enough against a wide variety of insects
•   Nonirritating to the skin when it is put on
•   Odorless or has pleasant odor
•    No effect on clothing after application (i.e. staining, bleaching, weakening of fibers)
•    No oily residue on skin and resists removal by wiping, washing, or sweating
•   Inert to commonly used plastics
•   Chemically stable
•   Economical for broad use by all
•   Non-toxic

7. What is(are) the safest and most effective product(s)?

• The Environmental Protection Agency (EPA) and Centers for Disease Control and Prevention (CDC) recommend products that contain either DEET (N,N-diethyl-m-toluamide) or Picaridin (KBR 3023) as the active ingredients of insect repellents. These have been shown to have the best efficacy in clinical trials. Products with these active ingredients typically offer longer-lasting protection than others.

• Oil of lemon eucalyptus [active ingredient: p-menthane 3,8-diol (PMD)] and oil of citronella are plant-based repellents. When used against mosquitoes in the US, scientific trials have found that they provide protection similar to insect repellents containing low DEET concentrations.

• The amount, or percentage (%), of the active ingredient makes all the difference in an insect repellent product. When comparing two products, make sure you are looking at the same active ingredient. Typically, the higher the percentage of the active ingredient a product contains, the longer the protection from mosquitoes. However, the concentration of different active ingredients cannot be directly compared (for example, 10% concentration of one ingredient doesn’t mean it works exactly the same as 10% concentration of another ingredient).

8. What are the different kinds of insect repellents available over-the-counter (OTC)?

There are MANY different brands of products available in the pharmacy. Read the label carefully for instructions on how to properly use the insect repellent. Find out what the active ingredient is and how much of it the product has. See Tables 1 and 2.

Table 1. Main ingredients and products names

Main ingredient Products

DEET Cutter, Cutter Backwoods, Cutter Backyard, Cutter Deep Woods,

Skedaddle, Skinastic, OFF!, Muskol, Outdoorsman, Sawyer, Ultrathon

Picaridin Repel, Off Skintastic
Lemon eucalyptus oil Cutter Advanced, Cutter Advanced Sport
Citronella oil Buzz Away, Green Ban, Herbal Armor, Natrapel

9. What are the differences between the products, brand vs. generic/store brands?

There are no known significant differences between brand, generic, or store brand insect repellents. The active ingredients of and past experiences with the most effective products should determine what you should buy and use.

10. Why are there so many different products?
Different products contain different concentrations of the main ingredient. A product should be chosen based on the duration of protection needed (from 20 minutes – 8 hours). See Table 2 for more information. Additionally, certain characteristics such as odor, sticky/greasiness, irritation, and potential damage to clothing and plastics differ between the products.

Table 2. Main ingredients with concentrations and their duration of action

Main ingredient              Concentration           Duration of Action
DEET 5 - 7%                     Up to 2 hours
DEET                                    10 - 30%                  Up to 6 hours
Picaridin                                 5 – 7 %                     Up to 4 hours
Picaridin                                    15%                         Up to 8 hours
Lemon eucalyptus oil 10 – 30%                    Up to 4 hours
Lemon eucalyptus oil 40%                         Up to 6 hours
Citronella oil 5 – 15%              About 20 – 30 minutes

11. Where is the best place to find insect repellents?

Repellents are found at retail, discount, and drug stores. Larger selections may be found at "outdoor" stores.

12. Where should insect repellents be applied?

Insect repellents should be applied to clothing, especially if the material is thin enough for insects to penetrate through. They should be applied to any exposed areas of skin, but avoid sensitive places like the face. Avoid breathing in the repellent through the nose or mouth. Do not let it contact the eyes. This can cause painful irritation.

13. What should be done if a side effect or reaction happens?

• If the reaction is local (limited only to the skin) and is not severe (no skin breaking, blisters, or hives), the area can be washed thoroughly with plain water. Do not use soaps or other harsh to remove any excess repellent chemicals as they could worsen the irritation.

• If the reaction is more severe, skin breakdown, spreading skin reactions, or anything happens beyond the skin (difficultly breathing, fast heart beats, “feeling very sick”), call 911 emergency services or your local Poison Control Center at 1-800-222-1222.

14. What are some alternatives to chemical insect repellents?

• Children and adults can wear protective clothing with long pants and long sleeves while outdoors. Be sure to apply insect repellent on the clothing and not directly contact the skin. Mosquitoes may bite through thin fabric.

• Mosquito netting can be used over infant carriers. Make sure there are no holes in the netting or large openings/gaps in the carrier.

• Dispose of containers or clear areas with standing water (bird baths, outdoor waterproof tarps, etc.), that provide breeding places for mosquitoes. Avoid stagnant bodies of fresh water, i.e. marshes, wetlands, farm ponds, shallow lakes, retaining/drainage ponds, etc.

15. What medications, or other products, can interact with insect repellents?

There are currently no known prescription medications taken that interact with common insect repellents. When using other topical products with insect repellents, the insect repellent should be the LAST thing applied to offer the best protection against insects.

16. Can sunscreen be used with insect repellents?

• Yes. People can, and should, use both a sunscreen and an insect repellent when they are outdoors. It is recommended NOT to use a single product that combines insect repellent containing DEET and sunscreen. The instructions for use of insect repellents and use of sunscreen are different. In most situations, insect repellent does not need to be reapplied as frequently as sunscreen. While no recommendations are available at this time regarding products that combine other active ingredients and sunscreen, it is important to always follow the label on whatever product you are using.

• To protect from sun exposure and insect bites, you can also wear long sleeves and long pants and apply insect repellent to your clothing, rather than directly to your skin.

17. When should insect repellents be reapplied?

• A product should be chosen with the concentration of insect repellent that will allow you to stay outside for the desired time. Use Table 2 to serve as a guide for the expected duration.

• Insect repellent should only be reapplied if mosquitoes have started biting. Products state that frequent reapplication and saturation are unnecessary. Repellent should not be applied more than 3 times per day.

• Combination sunscreen/insect repellent products should be avoided since sunscreen needs to be reapplied every two hours and the insect repellent does not need to be applied this often.

18. How do I read an insect repellent product label?

The active ingredient and concentration is listed on the label. Additionally, important directions and precautions are listed on the label. The pharmacist is available to help understand the label.

19. How can I find more information?

• Environmental Protection Agency (EPA) Web site

• Center for Disease Control (CDC) Web site

• National Pesticide Information Center (NPIC) through their toll-free number, 1-800-858-7378 or their web site

References:

1.   Brown M, Hebert AA. Insect repellents: an overview. J Am Acad Dermatol. 1997 Feb;36(2 Pt 1):243-9.
2.   Elston DM. Insect repellents: an overview. J Am Acad Dermatol. 1998 Apr;38(4):644-5.
3.   Combemale P, Dupin M. Insect repellents. J Am Acad Dermatol. 1998 Apr;38(4):645.
4.   Roberts JR, Reigart JR. Does anything beat DEET? Pediatr Ann. 2004 Jul;33(7):443-53.
5.   Buka RL. Sunscreens and insect repellents. Curr Opin Pediatr. 2004 Aug;16(4):378-84.
6.   Flake ZA, Hinojosa JR, Brown M, Crawford P. Clinical inquiries. Is DEET safe for children? J Fam Pract. 2005 May;54(5):468-9.
7.   Katz TM, Miller JH, Hebert AA. Insect repellents: historical perspectives and new developments. J Am Acad Dermatol. 2008 May;58(5):865-71.

8. CDC web site for “Insect Repellant Use and Safety”: URL: http://www.cdc.gov/ncidod/dvbid/westnile/qa/insect_repellent.htm Accessed 7/9/2009

6-Feb-10 0:00 AM

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How Insect Repellents Work and What to Look For Before Buying