Insect repellents – The facts

It takes just one imperceptible bite for the transmission of what could be a life-threatening disease, which makes us ask: ‘How can such a tiny, fragile insect cause so much pain, suffering and annoyance?’ (Webb 2016)

So, to protect ourselves from potentially dangerous pests such as mosquitoes and ticks, we can dress the part – wear long-sleeves and full length trousers, closed in shoes and, while you are at it, avoid the use  of perfumes and scents. It also helps to know when and where these menaces might be found – daytime, night-time, indoors, rural settings etc. Fortunately though, aside from these useful measures, we also have the tried and tested protection which is offered by effective insect repellents.  

The primary choices for selecting an insect repellent are:

  • Those you apply directly on the skin: This is the most effective measure, depending on the product choice, but must be applied carefully and re-applied within a specific time frame.
  • Those applied to clothing: Impregnated or sprayed clothing offers limited protection for exposed skin, so works best in combination with skin applications for complete coverage.
  • Aerosol room sprays: May keep most bugs at a distance, but not effective in windy conditions or if you are moving about.
  • Wearable devices: Have been proven to only offer minimal protection around the area of the body where the product is worn.

Care must be taken when choosing a personal insect repellent as product efficacy varies greatly. 

It is also important to note that re-application times of all products are only estimates as they can be affected by activities, climate or perspiration.

 

DEET

DEET is the acronym for N,N-Diethyl-m-toluamide which is a highly effective insect repellent. When applied correctly with direct application to the skin, DEET forms a vapour barrier at the skin surface that deters mosquitoes from landing on the skin.

Efficacy: A higher percentage of DEET does not necessarily mean better protection. Instead it identifies how long the protection may last, usually under ideal conditions.

Less than 10% DEET lasts about 2 hours, while 20-40% DEET gives 4-6 hours of protection.

In higher-risk areas of potentially fatal diseases such as malaria or dengue fever, 15–30% DEET is recommended.

Precautions: DEET can be safely applied to cotton, wool and nylon, but may damage spandex, rayon, acetate and pigmented leather.

DEET is also used in the production of some paints, plastics and synthetic fibres. If skin treated with DEET, or the product itself comes into contact with an item made of plastic and vinyl (e.g. sunglasses frames, watch bands, cell phones), it can cause damage to that article.

Recommendation: DEET is recommended for use in areas of endemic or epidemic mosquito-borne disease.

 

PICARIDIN

Picaridin is a synthetic chemical version of a repellent named piperine, found in pepper plants. Picaridin repels insects by forming a vapour barrier on the skin surface, blocking the bugs from sensing their prey (you/us).

Efficacy: A higher percentage of Picaridin does not offer greater protection, but instead determines how long the protection lasts.

Less than 10% Picaradin lasts about 2 hours, 10-20% lasts 3-4 hours

Recommendation: Picaridin is also recommended for use in areas of endemic or epidemic mosquito-borne disease.

 

CIDRIODIOL (Lemon eucalyptus or PMD)

Citriodiol is a natural product, but it is not the essential oil of Corymbia citridora leaves that provides protection, it is a by-product of the distillation process that gives the repellency, known as PMD.

Efficacy: Citriodiol has been shown to be as effective as DEET and Picaridin, although it generally requires higher doses for comparable protection and may need to be applied more frequently.

30% Citriodiol provides 2 hours protection.

Recommendation: Citriodiol is also recommended for use in areas of endemic or epidemic mosquito-borne disease.

 

PERMETHRIN

Permethrin is a synthetic chemical version of pyrethrum, which is derived from the chrysanthemum flower and has insecticidal properties (it kills insects by affecting their nervous system). Permethrin is odourless, vapour-free, and safe for all ages.

Permethrin is used in a number of ways to control insects: the product is available in various forms such as liquids, powders, dusts, aerosol solutions, sprays and on pre-treated clothing. 

Treated fabrics:

If added to water, or sprayed on, permethrin can be used to impregnate almost any material. Any insect that lands on the treated material dies before it can bite – this can be particularly useful in the case of sand flies which are one-third the size of a mosquito (and can fit through the holes of a mozzie net). In some parts of the world, sand flies play an important role in the transmission of the disease leishmaniasis.

Efficacy on fabrics:

  • Not regularly laundered: Permethrin-impregnated fabrics that are rarely washed (think mosquito net) have an effective period of between 3 and 6 months.
  • Frequently laundered: Permethrin-treated clothing retains its efficacy for 5-10 normal washes in hot or cold water and can be ironed.

Precaution: although rare, some people may experience a rash from wearing permethrin-treated clothing.

Recommendation: Permethrin is recommended for use in areas of endemic or epidemic mosquito-borne disease, in combination with an effective skin repellent.

Other uses:

Permethrin is also used in large public health mosquito control programs, on food and feed crops, on livestock and pets or in structures and buildings and may also be used in places where food is handled.

 

COILS, STICKS & CANDLES FOR BURNING

Mosquito coils and sticks that contain insecticides will kill mosquitoes, and those that contain citronella will repel mosquitoes or reduce the probability of bites.

Efficacy: evidence shows that when used outdoors, they will assist in reducing the number of bites. However in areas of endemic or epidemic mosquito-borne disease, they should not be relied upon solely for protection.

Precautions: Consideration should be given when burning these products indoors as the smoke may be inhaled in more concentrated amounts in enclosed areas.

Not recommended for use in areas of endemic or epidemic mosquito-borne disease unless in combination with skin repellent applications.

 

BOTANICAL BASED OR ESSENTIAL OIL REPELLENTS

Most natural bug repellent products are essential oil-based, with some only offering protecting against certain insects, and/or only for a very limited amount of time.

Efficacy: Eucalyptus oil, Melaleuca, < 10% Citronella provide 1 hour of protection.

Recommendation: Not recommended for use in areas of endemic or epidemic mosquito-borne disease.

 

WRIST/ANKLE BANDS

All contain a botanical-based product.

Efficacy: Studies show there was a reduction in total bites close to the bands, but there is no evidence that they can create a ‘halo’ of protection to all areas of the body.

Recommendation: Not recommended for use in areas of endemic or epidemic mosquito-borne disease.

 

GARLIC & VITAMIN B

There is nothing you can eat or drink that's been scientifically proven to prevent mosquito bites.

 

ULTRASONIC DEVICES & SMARTPHONE APPS

Devices and apps that claim to emit an ultra-sonic sound that repels mosquitoes, however there is no evidence to suggest this is effective.

 

IF IN DOUBT, CHECK APVMA

It is a legal requirement in Australia for all insect repellents to be registered with the Australian Pesticides and Veterinary Medicines Authority (APVMA) (external). Check the product label for an APVMA approval number to ensure it is registered and meets Australian safety standards.

You can also search for the product in the Public Chemical Registration Information System (PubCRIS) database (external).  

DEET, Picaridin, Permethrin, Citriodiol (lemon Eucalyptus oil or PMD) all have APVMA registration.

 

OF NOTE -

  • SUNSCREEN WITH REPELLENT

Products combining sunscreen and insect repellent are not recommended as sunscreen generally needs to be reapplied more often than insect repellent.

Don’t forget though… Apply the sunscreen first, then the repellent.

  • USING INSECT REPELLENTS SAFELY ON INFANTS & CHILDREN

0-3 months old: Insect repellents should not be used on babies under three months old – instead keep the infant in a pram covered with netting if you’re in an area where mosquitoes are a problem.

3 months+: Follow the instructions on the product label, look carefully at the level of DEET or picaridin in the product and use the repellent only as directed by the manufacturer.

  • Roll-on preparations are preferable to sprays.
  • Apply sparingly to exposed skin.
  • Do not use on cuts, wounds or irritated skin.
  • Do not apply to areas around the eyes or mouth.
  • Do not apply to the hands or fingers of young children.
  • When returning indoors, wash repellent off skin with soap and water.
  • Store repellents out of the reach of children.
  • ADVERSE REACTIONS: Repellents are considered safe when applied correctly. However, if you experience a serious reaction, consult a GP or call the Poison Information Centre Australia on 13 11 26.

Other insect bite prevention measures:

While travelling - https://www.travelvax.com.au/holiday-traveller/travel-tips/insect-bite-prevention

Around the home -

  • Cover all containers that store water (including swimming pools, septic tanks and similar) so that mosquitoes can't lay their eggs.  
  • Empty or drain containers (pots, watering cans) when they are not being used.
  • Change water in bird baths and watering troughs at least once a week.
  • Fill large holes in trees with sand or mortar.
  • Remove excess vegetation from garden ponds and stock with fish.
  • Do not over-water the garden.

 

References:

US Centers for Disease Control & Prevention (CDC): https://www.cdc.gov/ncezid/dvbd/about/prevent-bites.html

Department of Health, WA: https://ww2.health.wa.gov.au/Articles/N_R/Personal-insect-repellents

Dr Cameron Webb, Principal Hospital Scientist in Medical Entomology: https://medent.usyd.edu.au/RepellentGuidelines.pdf

USA Environmental Protection Agency : https://www.epa.gov/insect-repellents/deet

Oregon State University, USA: http://npic.orst.edu/factsheets/PicaridinGen.html

Royal Children’s Hospital, Melbourne:  https://www.rch.org.au/kidsinfo/fact_sheets/Insect_repellents_guidelines_for_safe_use/

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