From Cathy Wong,
Your Guide to Alternative Medicine.
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If you are looking for a natural mosquito repellent, you've probably noticed that there are many natural topical products available, all with different active ingredients. So which one works?

Lemon eucalyptus oil

The most effective natural mosquito repellent at the time of writing is Repel Lemon Eucalyptus.

• A 2002 study in the New England Journal of Medicine compared different synthetic chemical and herbal repellents:
  
  Repel Lemon Eucalyptus Repellent provided 120.1 minutes of mosquito protection, more than a repellent with a low concentration of the chemical DEET (Off Skintastic for Kids with 4.75% DEET provided 88.4 minutes of protection) and less than Off Deep Woods with 23.8% DEET, which provided 301.5 minutes of protection.
  
  
• A study by the US Department of Agriculture compared four synthetic mosquito repellents and eight natural mosquito repellents and found that Repel Lemon Eucalyptus was the most effective repellent, more so than a 7% DEET repellent.
  
  
• Lemon eucalyptus oil repellents, in addition to the chemicals DEET and picaridin, have been registered with the U.S. Environmental Protection Agency (which means that the materials have been reviewed and approved for effectiveness and human safety) and recommended by the Centers for Disease Control and Prevention (CDC) for mosquitoes that may carry the West Nile virus.
  
  
• A June 2006 Consumer Reports article stated that after conducting their own tests, Repel Lemon Eucalyptus was the best non-DEET mosquito repellent. However, volunteers criticized its odor.

Repel can be found online or is available at REI, Target and Wal-Mart.

Geranium oil and soybean oil

A repellent called Bite Blocker ranks second.

The New England Journal of Medicine study found that Bite Blocker provided 94.6 minutes of protection against mosquitos. This is slightly more effective than Off Skintastic for Kids (containing 4.75% DEET), which provided 88.4 minutes of protection.

The study by the United States Department of Agriculture ranked Bite Blocker number two in effectiveness after Repel. Bite Blocker was rated more effective than a synthetic 7% DEET mosquito repellent.

Bite Blocker contains the oils of geranium, soybean and coconut and is available as a spray or lotion. It can be purchased online at the Bite Blocker website for about $9 per bottle.

Citronella

A well-known natural mosquito repellent. The oils from the plant are used to make lotions, sprays, and candles.

A University of Guelph study assessed the effectiveness of 3% citronella candles and 5% citronella incense in protecting subjects from bites.

They found that subjects who were positioned near the citronella candles had 42.3% less bites and those near the citronella incense had 24.2% fewer bites.

Based on these results, citronella candles shouldn't be used as a stand-alone repellent, all though they may help in combination with topical repellents.

Other natural mosquito repellents

Although the above repellents are the most promising, there are other natural mosquito repellents that are being researched:

• Fennel - A small study by researchers at Seoul National University in Korea found that a spray mosquito repellent containing 5% fennel oil was 84% effective after 90 minutes and a repellent cream with 8% fennel oil was 70% effective after 90 minutes.
  
  
• Thyme - In one study, carvacrol and alpha-terpinene, two compounds derived from the essential oil of thyme, were found to have significantly greater repellency than a commercial DEET repellent. The researchers suggest that a spray made with 2% alpha terpinene is a promising natural mosquito repellent. However, don't try to make a thyme oil repellent at home- it is too irritating and strong-smelling to be used at effective concentrations above 25%.
  
  
• Clove oil - Two studies have found that undiluted topical clove oil is active against mosquitoes. However, like thyme oil, clove oil should not be applied undiluted to skin as a homemade repellent.
  
  
• Celery extract - A Thai study compared 15 mosquito repellents with a topical extract from celery. The researchers found that the extract did not irritate the skin or cause a burning sensation. It was found to be active against a wide range of mosquito species comparable to a 25% DEET formula.
  
  
• Neem oil - An extract from the tropical neem tree, neem oil has insecticidal compounds called azadirachtins.
  
  
• Vitamin B1 - Vitamin B1 is often taken to help repel mosquitos but one study suggests this remedy may be useless. Researchers at the University of Wisconsin study tested B1 with a larger sample of human subjects and found no effect of vitamin B.
  
  
• Garlic - Another popular theory is that ingesting garlic can provide protection against mosquitoes. A University of Connecticut study examined this claim with a randomized, double-blinded, placebo-controlled crossover study. The data didn't provide evidence of significant mosquito repellence. However, subjects only consumed garlic once, and the researchers say that more prolonged ingestion may be needed.