Which mosquito repellent ingredients work in Singapore, and what is the difference between DEET, picaridin, IR3535, citronella, mosquito coils and electric vaporisers? Singapore’s National Environment Agency (NEA) explains that NEA-registered topical repellents contain DEET, picaridin (icaridin) or IR3535. These ingredients help reduce bites by interfering with mosquitoes’ ability or tendency to approach treated people; their effects depend on the chemical and formulation. Some spatial repellents release repellent ingredients into surrounding air, such as those used in certain coils or electric devices. Repellents are not the same as medicines, vaccines or mosquito-breeding control. The most useful protection is the correctly registered product used according to its label, combined with appropriate clothing, screening and reduction of mosquito breeding habitats. NEA notes that the named synthetic topical ingredients generally provide longer-lasting protection than botanical formulations such as citronella or eucalyptus oils.
For Hougang families and Secondary Science students researching dengue prevention, repellent Chemistry, safe mosquito sprays for children, why perfume does not work as a mosquito repellent, volatility, concentrations and skin-product labels, begin with four questions: Is it a topical or spatial product? Which active ingredient is registered and named? What usage and age restrictions are stated? How long does the label say the protection lasts under the relevant conditions? NEA advises applying sunscreen before repellent where both are used, following all product directions, not allowing children to apply repellent themselves, and prioritising physical measures such as clothing or nets for children under two where possible. This article teaches molecule-and-formulation reasoning; it does not provide a recipe for repellent, recommend an unsupported concentration or replace the official product label.
A mosquito can find a person without reading a street sign
Imagine sitting in a Singapore garden. The air seems still, and there is no obvious source of mosquitoes nearby. Yet one may find an exposed arm. Many mosquitoes rely on a combination of cues that can include carbon dioxide, body odours, heat and visual signals. They do not identify a person the way humans recognise a face. Repellents can influence that sensory encounter, making a treated host less attractive or harder to approach under the relevant conditions.
That is a wonderful Chemistry problem: a small amount of a particular molecule changes a real biological behaviour. It shows that molecules do not have to kill an organism to produce a useful effect. It also reminds us that chemistry interacts with biology, weather, human behaviour and proper product formulation.
The official NEA repellent categories
| Category | Where it acts | Example ingredient family | Important limit |
|---|---|---|---|
| Topical repellent | Applied to exposed skin or suitable clothing as labelled | DEET, picaridin or IR3535 in NEA-registered topical products | Coverage and protection duration follow the product label |
| Spatial repellent | Releases an appropriate chemical into surrounding air | Certain listed volatile pyrethroid ingredients | Performance depends on space, ventilation and product conditions |
| Physical measures | Avoids or blocks mosquito contact without topical active repellent | Screens, nets and protective clothing | Coverage must be appropriate to the activity |
| Breeding-site prevention | Reduces the production of new mosquitoes | Removal or management of stagnant-water habitats | Needs regular property and community action |
The NEA: Use of Mosquito Repellents identifies registered topical active ingredients and practical application rules. The NEA: Types of Spatial Repellents describes recognised spatial forms and safety concerns. The NEA: Stop Dengue Now places repellents within Singapore’s wider dengue-prevention strategy. These are distinct measures and no single one guarantees a mosquito-free environment.
DEET, picaridin and IR3535: three names, one shared purpose
DEET (diethyltoluamide), picaridin (also called icaridin) and IR3535 (ethyl butylacetylaminopropionate) are chemically different active ingredients. They are used in topical repellent formulations designed to reduce mosquito bites. Their molecular interactions with mosquito sensory systems and the details of each formulation can differ. It is better to describe their shared purpose accurately than to claim every active ingredient uses the exact same receptor or mechanism.
NEA-registered products have undergone relevant safety and efficacy assessment under the applicable registration framework. This does not mean all formulations are identical, that an ingredient guarantees full protection or that a product intended for adults may automatically be used on a young child. Read the specific registration and product label, including any limits on use.
Repellent versus insecticide: a distinction students should learn
A repellent reduces contact or biting behaviour in the intended use. An insecticide targets insects through a toxic or other pesticidal action. Some products and chemical families may show more than one biological effect depending on dose, organism and delivery, but consumers should follow the actual approved product’s purpose. Do not assume that a topical repellent is something one should spray on insects, or that a pesticide intended for a surface is safe to apply to skin.
This is a foundational scientific habit: chemicals must be understood in their actual formulation and authorised context. “Same chemical family” is not the same thing as “same use, concentration or safety instructions”.
What is a spatial repellent?
Spatial repellents act in the surroundings rather than being rubbed on the body. NEA describes mosquito coils, electric vaporisers or mats, and passive emanators among the forms. Relevant products can use ingredients such as metofluthrin, transfluthrin, prallethrin or related pyrethroids. How well they work depends on the formulation and the environmental setting.
A spatial product is not a harmless perfume device simply because it has no obvious liquid spray. NEA advises avoiding prolonged or close-range inhalation of fumes, providing good ventilation for indoor use, keeping products away from children and food, and not leaving coils or electric devices unattended. Follow those instructions instead of combining multiple devices without evidence of added benefit.
How do repellent molecules reach their target?
For some formulations, molecules are present at or near the treated skin or clothing surface; others can become available in the surrounding air. The chemical’s volatility, formulation, interaction with skin or fabric and environmental conditions influence how rapidly it moves and how long protection may persist. Sweating, getting wet, swimming or clothing friction can reduce effectiveness, as NEA notes.
A repellent’s smell is not a reliable numerical measure of protection. Some effective ingredients may not smell strongly to a person, and a strong fragrance does not establish repellent efficacy. The Why Perfume Smells Different Over Time explains the chemistry of fragrance volatility; this repellent guide asks the additional question of tested biological performance.
Worked example: a label percentage is not a protection-time promise
Question: A fictional product formulation contains 12 g of active ingredient in 100 g of total formulation. Calculate the mass percentage of active ingredient. Does that result alone tell us how many hours of mosquito protection the product provides?
Solution: Percentage by mass = (12 g ÷ 100 g) × 100% = 12% w/w. The result describes a formulation concentration, not how long the effect lasts. Protection depends on the particular ingredient, product formula, application conditions and relevant efficacy evidence. A student should never use this fictional percentage as instructions for preparing or applying mosquito repellent.
Transfer: Would a product with a greater number on its concentration label automatically be more suitable for every child? No. Suitability, safety and use conditions are determined by the registered product’s instructions and the user’s circumstances, not by ranking percentages alone.
Why a ‘natural’ essential oil is not automatically the better repellent
Some plant-derived substances have repellent activity, but “natural” does not mean “stronger”, “safer for everybody” or “longer lasting”. NEA says DEET, picaridin and IR3535-based topical repellents generally provide longer-lasting protection than botanical alternatives such as citronella and eucalyptus essential oils. NEA also notes that botanical repellents are not required to be registered in the same way as its registered topical chemical products.
A responsible comparison therefore looks at efficacy evidence, product quality, duration, user suitability and the specific label. Natural compounds can also cause irritation or allergic reactions. Do not use a homemade essential-oil blend as a substitute for a registered product solely because a social-media video describes it as chemical-free.
Why dengue prevention needs more than a bottle
Repellents can help reduce bites while they are being used properly, but mosquitoes reproduce in suitable standing-water habitats. Removing or preventing those breeding locations is a different part of prevention. In a household, screens and suitable clothing are useful physical barriers; for young children, NEA specifically highlights nets and protective clothing where possible.
This offers a helpful multi-layer model: reduce breeding, reduce exposure, and use registered repellents according to the label where appropriate. A student should not claim a single spray eliminates the need for the other measures, or that mosquito activity depends only on what time of day it is.
NEA’s safety instructions that matter for families
- Read and follow the product label, including the stated duration and reapplication rules.
- Use a product appropriate to the intended user; do not let children apply repellent on themselves.
- Avoid applying to cuts, wounds or irritated skin, and stop use if an allergic reaction occurs.
- For facial use, dispense onto hands first and avoid eyes and mouth, following NEA and product instructions.
- If using sunscreen, apply sunscreen first, followed by the repellent, as NEA advises.
- Wash hands after application and do not use expired products.
- For children under two, favour physical measures such as nets and protective clothing wherever possible.
- For spatial repellents, follow ventilation and equipment precautions and keep them away from children and food.
These are official general-use principles from NEA: Use of Mosquito Repellents. The most current product-specific directions and any individual medical considerations require the labelled information and suitable professional advice.
A fair-test question for Secondary Science
Suppose a fictional classroom dataset compares mosquito approaches toward two model surfaces in a supervised research simulation. If surface A has 40 approaches and surface B has 10 during otherwise comparable observation periods, the reduction relative to A is (40 − 10)/40 × 100% = 75%. This is a calculation on imaginary data, not a validated protection percentage for any real repellent. The experiment could have confounding factors, sampling variation and different conditions.
Students should ask whether the measurement counts approaches, landings or bites, how many trials were observed and whether exposure conditions were controlled. That is why the Secondary 1 Fair Tests and Variables is relevant: the dependent variable and experimental validity matter as much as the arithmetic.
Seven common misconceptions
| What the student says | What is missing | Better question |
|---|---|---|
| Repellents always kill mosquitoes | Repelling versus toxic action | What was the product designed and tested to do? |
| Stronger smell means longer protection | Fragrance versus measured efficacy | What does the registered label say? |
| All three active ingredients are identical | Chemical identity and formulation | Which named ingredient is present? |
| Higher concentration always makes a product suitable | Use restrictions and testing | What does the label permit? |
| Every plant extract is safer than synthetic ingredients | Hazard and efficacy evidence | What assessment supports the claim? |
| A spatial vaporiser works in every room regardless of ventilation | Environmental conditions and intended use | What precautions and limits are stated? |
| Repellents remove the need to prevent breeding | Multiple layers of prevention | What happens when protection wears off? |
How this fits a useful Hougang Science learning route
| Level | Science connection | What students can explain |
|---|---|---|
| Secondary 1–2 | Mixtures, variables, evaporation, measurement and evidence | Why a strong smell alone cannot prove repellent efficacy |
| Secondary 3–4 Chemistry | Molecules, polarity, formulation and chemical safety | Why ingredients with different formulas need different evidence |
| JC Chemistry | Intermolecular interactions, kinetics and quantitative data | How concentration, exposure and test conditions affect a scientific claim |
| Further study | Product testing, chemical biology and environmental health | How official efficacy and safety information supports decisions |
A three-pupil tutorial can have students interpret a different fictional dataset each, identify an unsupported conclusion and write an improved one. This is a realistic, safe way to learn Chemistry and scientific reasoning without exposing children or mosquitoes to DIY chemicals. The Why Mosquitoes Bite and Detect Hosts, Sunscreen Chemistry in Singapore and Chemical Safety, Product Labels and Risk provide useful sibling explanations. The Hougang Chemistry Learning Library is the main Hougang Chemistry learning reference.
Frequently asked questions
Which active ingredients does NEA list for registered topical mosquito repellents?
DEET, picaridin (icaridin) and IR3535. Check for an appropriate NEA registration mark and follow the exact product instructions.
Are mosquito coils and topical lotions the same product?
No. Coils and similar spatial devices release ingredients into surrounding air; topical formulations are applied to skin or suitable clothing according to instructions. Safety rules differ.
Should sunscreen go before or after mosquito repellent?
NEA advises applying sunscreen first and then repellent, following the relevant product labels.
Is citronella guaranteed to protect longer because it is plant-based?
No. NEA notes that the specified registered topical active ingredients generally provide longer-lasting protection than botanical products such as citronella and eucalyptus oils.
How should parents protect a child below two years old?
NEA recommends physical protective measures such as nets and suitable protective clothing where possible. Consult the product label and a qualified healthcare professional if individual advice is needed.
Can students make a DIY repellent and test it on themselves?
That is not recommended as a school or home activity. Use official product information and hypothetical datasets for learning; do not mix active chemicals or experiment on people.
Official NEA guidance and connected reading
- NEA: Use of Mosquito Repellents
- NEA: Types of Spatial Repellents
- NEA: Stop Dengue Now
- NEA: Registration of Public Health Repellents
- Why Mosquitoes Bite and Detect Hosts
- Why Perfume Smells Different Over Time
- Chemical Safety, Product Labels and Risk
- Hougang Chemistry Learning Library
Singapore-specific guidance checked against NEA information updated September 2026. This article is chemical and public-health literacy, not a recommendation of a specific product or a substitute for its registered label.