Kao Found that low-viscosity silicone oil combined with repellent ingredients such as citronella oil and DEET can greatly improve mosquito repellent effectiveness. This is because the repellent ingredients can be transferred directly to mosquitoes via low-viscosity silicone oil, and studies have found that even very low concentrations of repellent ingredients can protect against mosquito bites. The research results were presented at the 44th Annual Meeting of the Association for Chemoreception Sciences (AChemS, April 29, 2022, Florida, USA).
      As mosquito-borne infections such as malaria and dengue fever threaten the world, various measures are being taken to prevent them. Mosquito repellents are the most common mosquito countermeasure in households, but can sometimes be accompanied by a sticky and strong odor due to the different repellent ingredients. Therefore, if effective, convenient and comfortable mosquito repellents are available, the number of people using them will increase, and the risk of mosquito infections will be reduced.
      Kao reported the technology of applying low-viscosity silicone oil to make the surface of the skin to prevent mosquito bites. In the skin with low-viscosity silicone oil commonly used in cosmetics, mosquito feet are quickly soaked and spread, attracting mosquito feet, inducing escape actions and shortening the landing time of mosquitoes.
      Kao believes that by applying this unique mechanism of action, a new repellent can be developed to solve problems such as stickiness and smell. Therefore, in order to better understand the mechanism and usefulness of this repellent, the repellent effect of low viscosity silicone oil combined with commonly used repellent ingredients citronella oil and DEET was studied.
      To verify the effectiveness of the repellent materials, mosquitoes were observed in specialized cages. In a cage with 25 mosquitoes, the preparation of citronella oil (surface adhesion 4μg/cm²) with the concentration of 10/1-100/1 was put into the coated model forearm, and the landing action of mosquitoes on the forearm was observed. The results showed that the low concentration of citronella oil alone showed only weak avoidance effect. On the other hand, the combination of low viscosity silicone oil (surface adhesion 0.2mg/cm²) and low concentration of citronella oil significantly improved the avoidance of mosquitoes and significantly reduced the number of mosquitoes landing. In addition, this effect is the pivot point of dynamic observation of very low concentration DEET (surface adhesion 0.2μg/cm²) without showing effect alone.
      In order to find out the mechanism of this phenomenon, experiments were carried out to contact mosquito feet on the surface coated with low viscosity silicone oil and citronella oil. The results confirmed that the amount of citronella oil attached to the mosquito's feet was higher than that of the citronella oil monomer. It showed that when the mosquito landed on the surface, the low viscosity silicone oil quickly soaked and spread to the mosquito's feet, and the citronella oil and the low viscosity silicone oil also transferred to the mosquito's feet. In addition, this phenomenon is unique to low viscosity silicone oils and is not found in substances such as glycerin.
      Mosquitoes are known to use sensory receptors on their feet to pick up chemicals. When citronella oil is transferred to the mosquito's legs, sensory receptors in the feet detect it, and the mosquito may find the surface more annoying. By coating people's skin with citronella oil, or DEET, in combination with low-viscosity silicone oil, it can reduce the number of mosquito bites.
      Even low concentrations of citronella oil and DEET can be combined with low viscosity silicone oil to avoid mosquito research, which is expected to be used in the development of excellent mosquito repellents. Since low-viscosity silicone oil is widely used in cosmetics, it is more comfortable to apply than existing repellents. Even a small amount of repellent can be effective, thus reducing the strong smell and the burden of use, and creating an easy-to-use repellent is more likely.