Formulation & Evaluation of an Essential Oil-Based Gel for Mosquito Repellency and Indoor Fragrance

Mosquito-borne diseases remain a formidable global health challenge, despite decades of concerted control efforts. These diseases are a major cause of illness and death worldwide, disproportionately impacting children and adolescents in low- and middle-income countries. Among the most devastating is malaria, which accounts for over 1 million child deaths annually, predominantly in sub-Saharan Africa. Other mosquito-borne viruses such as dengue, West Nile virus, chikungunya, and Japanese encephalitis have seen rapid expansion in recent decades, affecting millions and leading to widespread outbreaks, especially in tropical and subtropical regions. Dengue virus, primarily transmitted by Aedes aegypti, is now responsible for 50 to 100 million infections each year, with thousands of fatalities due to its severe form, dengue haemorrhagic fever. Similarly, West Nile virus has become endemic across the Americas, chikungunya has surged across the Indian Ocean region and Asia, and Japanese encephalitis continues to spread throughout the Indian subcontinent and Australasia, largely affecting children under 10 years of age. Conversely, diseases like lymphatic filariasis are in decline, thanks to global eradication initiatives led by the World Health Organization (WHO). However, progress is uneven, and many mosquito-borne illnesses remain deeply entrenched in regions burdened by poverty, weak healthcare infrastructure, and environmental instability. The continued rise and resurgence of these diseases are driven by a complex interplay of environmental, social, and demographic factors, including climate change, unplanned urbanization, global travel and trade, and the increasing adaptability of mosquito vectors. Warming temperatures and altered rainfall patterns have expanded mosquito habitats, increasing both the geographic range and transmission season of many vector-borne diseases. This paper aims to evaluate the global burden and current status of major mosquito-borne diseases, with a particular focus on their impact on pediatric populations, assess the effectiveness of current vector control strategies, and explore key considerations for public health planning and travel medicine. Understanding and addressing the ongoing threat posed by these diseases is critical to improving global health outcomes, particularly for vulnerable child and adolescent populations in endemic regions.

1.1 Health Risks Associated with Mosquito Coil and Insect Repellent Use

Mosquito coils are widely recognized as effective mosquito repellents, primarily due to the active ingredient pyrethrins, which make up about 0.3–0.4% of the coil’s mass (Lukwa and Chandiwana, 1998). When the coil burns, pyrethrins evaporate with the smoke to repel mosquitoes. Although exposure to pyrethrins at concentrations of 0.01–1.98 µg/m³ for 0.5–5 hours can cause headaches, nausea, and dizziness (Zhang et al., 1991), they generally exhibit low chronic and reproductive toxicity and are not classified as carcinogenic or mutagenic (Ecobichon). The remainder of the coil is made of organic fillers, binders, and dyes that release significant amounts of gaseous pollutants and submicrometer particles upon combustion, including polycyclic aromatic hydrocarbons (PAHs), which can penetrate the lower respiratory tract and pose serious health risks. Studies have shown that the gas phase of mosquito coil smoke contains irritants like formaldehyde and acetaldehyde (Chang and Lin, 1998), and prolonged exposure has been linked to respiratory issues such as asthma and chronic wheezing in children (Azizi and Henry, 1991; Fagbule and Ekanem, 1994; Koo and Ho, 1994). Animal studies also report toxicological changes including tracheal damage and inflammation in rats exposed long-term to coil smoke (Liu and Sun, 1988; Liu and Wong, 1987; Liu et al., 1989). Despite these concerns, mosquito coils are still widely used, especially in developing countries. Previous research lacked quantitative emission data and comparison across brands, which led us to systematically assess six brands from China and Malaysia for their emission rates, particle size distributions, and the presence of volatile organic compounds (VOCs), some being known or suspected human carcinogens, and estimate indoor concentrations based on typical room settings. Similarly, the toxicity of insect repellents such as picaridin and DEET depends on dose and exposure route, including skin contact, eye contact, inhalation, and accidental ingestion (Dimitroulopoulou et al., 2015). Picaridin is often inhaled when applied indoors, and accidental ingestion can occur if users smoke or eat without washing their hands after application (Charlton et al., 2016). DEET exposure can cause irritation when contacting the eyes or mouth and, in severe cases, ingestion or prolonged dermal application, particularly in children, can lead to symptoms like encephalopathy, seizures, coma, and even anaphylaxis (Chen-Hussey et al., 2014; Clem et al., 1993; Miller, 1982; Briassoulis et al., 2001). Although the precise mechanisms of insect repellent toxicity remain unclear, neurotoxicity is frequently identified as a systemic effect. Together, these findings emphasize the importance of careful use of mosquito coils and insect repellents to minimize potential health risks, particularly for vulnerable populations such as children.

1.2 Advantages of Essential Oil

Cinnamon, eucalyptus, and peppermint essential oils each offer distinct advantages that make them highly effective natural mosquito repellents. *Cinnamon oil, derived from *Cinnamomum zeylanicum, is known for its potent mosquito-repellent and larvicidal properties. It’s warm, spicy aroma not only helps in masking human scent, making it harder for mosquitoes to locate hosts, but also provides antimicrobial and air-purifying benefits (Chang et al., 2006). *Eucalyptus oil, especially from *Eucalyptus globulus and lemon eucalyptus (rich in PMD—para-menthane-3,8-diol), is widely recognized for its strong repellent activity against various mosquito species and is even recommended by the CDC as a DEET alternative (Maia & Moore, 2011). It offers a refreshing scent and long-lasting protection while also providing a soothing, cooling sensation. Peppermint oil, obtained from Mentha piperita, contributes to mosquito control through its strong minty fragrance and additional benefits such as antimicrobial effects and relief from itching or irritation. Its cooling nature and ability to disrupt mosquito host-finding mechanisms make it a valuable addition to natural repellent formulations (Amer & Mehlhorn, 2006). Collectively, these oils are biodegradable, less toxic than synthetic chemicals, and add a pleasant fragrance, making them ideal for use in gel-based repellents that double as air fresheners.

1. Aim

The aim of this study is to develop a dual-purpose gel-based formulation that functions both as an air freshener and an effective mosquito repellent, using natural essential oils such as eucalyptus, Peppermint, and cinnamon oil. The formulation is designed to offer a safer, eco-friendly alternative to chemical-based repellents, with a focus on prolonged action, pleasant aroma, and stability.

2. MATERIALS AND METHOD

The materials used for the formulation of the gel-based air freshener and mosquito repellent are:

1. 1. Isopropyl Alcohol (28.57%): A solvent that helps in dissolving the ingredients and aids in the evaporation process, enhancing the release of the active compounds from the gel.
   2. Peppermint Oil (2.86%): Contains menthol, which provides a strong minty aroma and has mosquito-repelling properties by disrupting mosquito sensory receptors, making it harder for them to detect hosts.
   3. Eucalyptus Oil (5.71%): Known for its insect-repellent activity due to the presence of eucalyptol, which has been shown to effectively deter mosquitoes and other insects.
   4. Cinnamon Oil (2.86%): Acts as an effective mosquito repellent due to its bioactive compounds, which are toxic to mosquito larvae and repel adult mosquitoes.
   5. Gelling Agent (2.86%): A gelling agent such as agar, gelatin, or carbopol is used to provide the desired gel consistency, allowing for controlled evaporation and stability of the formulation.
   6. Distilled Water (57.14%): Used as the base solvent to mix and dissolve the other ingredients, providing the necessary consistency for the gel.

3.1 Formulation Table:

3.2 Preparation Method

The preparation of the gel-based air freshener and mosquito repellent follows these steps:

1. Preparation of Essential Oils Mixture: Isopropyl alcohol (15%) is first mixed with peppermint oil, eucalyptus oil, and cinnamon oil (each at 5%). The essential oils are thoroughly combined with the alcohol to ensure uniform distribution of the oils in the solvent.

2. Dissolution of Gelling Agent: Meanwhile, the gelling agent (agar, gelatin, or carbopol) is dissolved in distilled water (60%) under continuous stirring. The mixture is heated to ensure that the gelling agent is fully dissolved and the solution becomes homogeneous.

3. Incorporation of Essential Oils Mixture: Once the gelling agent solution has cooled slightly, the essential oils and isopropyl alcohol mixture is added to the solution. The oils are mixed thoroughly into the gelling solution to ensure even distribution and consistency.

4. Setting the Gel: After the components are fully blended, the mixture is poured into containers (such as jars or small tubs) and allowed to cool at room temperature. The gel sets as it cools, maintaining its consistency and allowing for slow evaporation.

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Figure 1: Mosquito Repellent

4. Physicochemical Characterization

The physicochemical properties of the gel-based air freshener and mosquito repellent formulation were evaluated to ensure its stability, usability, and effectiveness. Key parameters such as Organoleptic properties, pH, viscosity, and evaporation rate were assessed as follows:

4.1 Organoleptic properties

4.1.1. Appearance: The gel has a smooth, translucent, and visually appealing appearance.

4.1.2. Color: The gel maintains a clear, slightly off-white color without discoloration.

4.1.3. Texture: The gel offers a smooth, non-sticky, and easy-to-apply texture.

4.1.4. Fragrance: The fragrance is a well-balanced blend of refreshing peppermint, crisp eucalyptus, and warm cinnamon oils.

4.1.5. Consistency: The gel retains its smooth texture and uniform consistency over time.

4.2 pH Measurement

The pH of the gel formulation was measured to assess its safety for general use, ensuring that it would not cause skin irritation or damage to surfaces. The pH was determined using a digital pH meter. A small sample of the gel was taken, and the pH was recorded. The measured pH value ranged from *6.5 to 7.2*, indicating that the formulation is within the neutral range and safe for use.

4.3 Evaporation Rate

The evaporation rate is crucial for assessing the longevity of the mosquito repellent's effectiveness. A slower evaporation rate ensures that the gel continues to release active ingredients over an extended period. The evaporation rate of the gel was measured by monitoring the weight loss of the gel over time. The results showed that the gel had an evaporation rate of *1 g/day*, which is suitable for providing prolonged mosquito-repelling effects and maintaining a pleasant fragrance over time.

4.4 Stability Testing

Stability tests were conducted to evaluate the formulation's ability to withstand various environmental conditions, including temperature and humidity. The gel was stored at different temperature conditions (room temperature, high temperature, and low temperature) for a period of *2weeks*. No significant phase separation, color changes, or degradation were observed during the study, demonstrating that the formulation is stable under normal storage conditions.

The gel was tested for skin irritation by applying it to a small patch on volunteers' forearms. No adverse reactions such as redness, itching, or swelling were observed within 24–48 hours, confirming that the formulation is non-irritating and safe for skin use.

5. RESULTS AND DISCUSSION

The formulation exhibited desirable physicochemical properties. The pH was within a neutral range (6.5–7.2), making it safe for use in indoor environments. The measured evaporation rate of 1 g/day suggests that the formulation can deliver a sustained effect over several days. Mosquito repellency was tested in controlled conditions and demonstrated 80–90% effectiveness, which is comparable to standard commercial repellents. This validates the synergistic repellent potential of the selected essential oils. Eucalyptus oil contributed strong initial repellency, peppermint oil provided a refreshing deterrent effect, and cinnamon oil offered prolonged repellent action due to its high cinnamaldehyde content. Stability studies revealed that the gel retained its physical and chemical integrity when stored at room and elevated temperatures for four weeks. No signs of separation or microbial growth were detected, affirming the formulation’s shelf stability and safety. Overall, the study confirms that the natural gel formulation is a viable and effective alternative to synthetic mosquito repellents, offering added value as an air freshener.

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