Mosquitoes are more than just a nuisance; they transmit various diseases that pose serious health risks. These illnesses include Zika, West Nile virus, dengue, and malaria, affecting millions globally each year. Chemical repellents offer a primary defense against these biting insects, helping to reduce exposure and the spread of such diseases.
Common Synthetic Repellent Chemicals
N,N-Diethyl-meta-toluamide, known as DEET, is a synthetic insect repellent developed by the U.S. Army in 1946 and publicly registered in 1957. It is effective against mosquitoes, ticks, and flies. Available in concentrations from 5% to 100%, higher concentrations, such as 30-50%, provide longer protection, up to 12 hours.
Picaridin, also known as icaridin, is a synthetic compound developed in the 1980s and available in the U.S. since 2005. It is odorless, non-greasy, and does not damage plastics or synthetic fabrics, unlike DEET. A 20% concentration has shown comparable or superior efficacy to DEET against mosquito species, providing up to 12 hours of protection against mosquitoes and ticks.
IR3535, developed by Merck KGaA, has been widely used in Europe for over 30 years. The U.S. Environmental Protection Agency (EPA) recognizes IR3535 as a biopesticide because it is structurally similar to a naturally occurring amino acid. This colorless and odorless oil is gentle on the skin and typically offers protection for several hours, with 20% formulations providing up to eight hours against mosquitoes and even longer against ticks.
How Repellent Chemicals Deter Mosquitoes
Mosquito repellent chemicals work by interfering with a mosquito’s ability to locate a host, rather than killing them. They create a vapor barrier on the skin, deterring mosquitoes from landing and biting. Active ingredients interact with the mosquito’s sensory system, especially olfactory receptors on their antennae.
DEET is thought to confuse or inhibit olfactory receptors, making it difficult for mosquitoes to detect human scents like lactic acid and carbon dioxide. Research suggests DEET directly activates certain odorant receptors or may mimic plant defensive compounds. This disrupts their “odor code,” preventing mosquitoes from identifying a blood meal.
Picaridin also appears to block mosquitoes from sensing their prey by stimulating sensory hairs on their antennae, preventing them from recognizing host cues. For IR3535, its repellent effect is believed to be related to the insect’s intolerance to its odor, though exact molecular interactions are still being investigated. This mechanism ensures mosquitoes move away from treated areas without being harmed.
Safe Use and Application
Following product label instructions is important for safe and effective use of mosquito repellents. Check active ingredients and concentrations for suitability to your needs and age group. For example, DEET concentrations up to 30% are recommended for children over two months old.
Apply repellent only to exposed skin and the outside of clothing; avoid applying it under clothing. When applying to the face, spray a small amount onto your hands first and then rub it onto the face, avoiding eyes, mouth, cuts, wounds, or irritated skin. Do not apply repellent to children’s hands, as they may put them in their mouths or eyes.
Reapplication frequency depends on the product’s concentration and environmental factors such as sweating or swimming. Reapply if sweating heavily or swimming to maintain protection. Once indoors, wash treated skin with soap and water and wash treated clothing to remove residue.
Plant-Based Repellent Alternatives
Plant-derived compounds offer alternatives to synthetic repellents, with some recognized by regulatory bodies. Oil of Lemon Eucalyptus (OLE), which contains the active ingredient p-menthane-3,8-diol (PMD), is a popular choice, formed from a modification of sustainably harvested Eucalyptus citriodora oil. OLE products, especially those with 30-40% PMD, can offer up to six hours of protection and have comparable efficacy to lower concentrations of DEET.
Citronella, derived from herbs, is a common plant-based repellent found in candles and sprays. While citronella oil alone offers limited protection, lasting about 19 minutes on the skin, its effectiveness can be prolonged to at least 3 hours when combined with other compounds like vanillin. Proper formulation is important for its efficacy, as it can evaporate quickly.
Geraniol, found in plant oils like citronella, lemongrass, and rose, is used as a fragrance or flavor, in addition to its repellent properties. As a repellent ingredient, it can be effective for 2 to 4 hours against mosquito species, depending on the concentration and formulation. Studies show geraniol can have more repellent activity than citronella or linalool in indoor and outdoor settings.
Catnip oil has shown strong repellent properties against mosquitoes. Research indicates that catnip oil can be highly effective, sometimes even more potent than DEET in initial repellency, though its duration of effect is shorter. This natural oil also demonstrates efficacy against other pests like stable flies and house flies.