Mosquito Repellents: What Works And What Does Not Work.

My last post on electronic mosquito repellents prompted me to do some research on the different types of mosquito repellents. There are several  diseases in PNG that are transmitted by mosquitoes – malaria, dengue fever, elephantiasis and Japanese encephalitis. There may be other animal diseases also transmitted by mosquitoes but I am not familiar with animal diseases. There are now many companies producing mosquito repellents for use in-doors as well as outside homes. Therefore, I thought it would be a good idea so do some reading on the types of repellents available on the market. And find out which ones actually work and which does not not as indicated by laboratory or field studies.

How does a repellent work?

Female mosquitoes need blood to ensure their eggs develop properly. Its part of the biology of the mosquito, unfortunately for us, this blood meal means disease for us. When having a blood meal, the female mosquito releases her saliva into the biting area. The saliva contains substances that prevent the blood from clotting so that the mossie can suck easily. Some people who have sensitive skin are allergic to mosquito bites because of these substances.

To prevent the female mosquitoes from landing on our bare skin to suck blood, we have to apply chemicals on the skin to make it unattractive for the mosquito. Repellents do not kill mosquitoes!

What kind of repellents work?

Based on well conducted research studies, for skin application, two chemicals have been shown to work best:

1. DEET (N, N-diethyl-m-toluamide)
2. Picaridin (KBR 3023)

A plant based product, oil of lemon eucalyptus has also been to shown to repel mosquitoes, similar to as when using low concentrations of DEET. For clothing, shoes and outdoor ware or camping gear, products containing permethrin have been shown to be effective.

How do I decide which product is best?

Read the label of the product carefully and note the concentration of the active ingredient or chemical. I have listed the two most effective ones above. Check their concentrations. The higher the concentration, the greater the protection. BUT, studies have shown that a concentration of higher than 50% of the chemical does not offer greater protection. As a rule of thumb, aim for products that has at least 20% of the active chemical.

However, having said that, you can compare the percentage concentration of DEET and picaridin. These are two different chemicals with different effective concentrations.

For clothing and other out-door gears, apply products (e.g. a spray) containing permethrin prior to leaving your home. DO NOT APPLY PERMETHRIN TO SKIN, FACE or EYES!

What about repellents with sunscreen?

There is no scientific literature on the effectiveness of repellents containing sunscreen. The Centres for Disease Control also does not recommend using repellents with sunscreen.

How effective are electronic repellents?

There is no evidence that EMRs are effective. There is also no strong data to support the use of devices which transmit sound waves to repel mosquitoes.

PRECAUTIONS

• Extra caution must be taken when applying chemical repellents on pregnant women, lactating mothers and on children.
• See your dermatologist if you have sensitive skin before applying any of the products.
• Always follow the instructions on the product label.
• Do not use repellents under clothing.
• Never use repellents over cuts, wounds or irritated skin.
• Do not apply to eyes or mouth. Apply sparingly around the ears.
• Do not use sprays directly on face. Spray on hand first then apply to face.
• Do not allow children to handle products.
• When using on children, apply to your hands first then put on the child. Do not apply on children’s hands.
• When returning home after use, wash skin with soap and water or bathe. Also wash treated clothes.
• If you or your child get a rash or any other kind of reaction from applying a repellent, stop using the product and wash the repellent off with soap and water. If you go to see a doctor, take the product with you to show to the doctor. 
• Oil lemon of eucalyptus are not recommended for children under three years.

References

Centre for Disease Control and Prevention website- USA.