Choosing The active ingredient
For a material to be valuable as a mosquito repellent, it must meet certain criteria :
  • effectively discourage insect attack on the treated area for hours and on different types of surfaces.
  • work under a variety of different environmental conditions.
  • not toxic or cause irritation when applied to human or animal skin.
  • it must be cosmetically acceptable, having a pleasant odor, taste, and feel.
  • harmless to clothing.
  • relatively low cost and effective against other common types of insects, such as flies.
The active ingredients contained in the mosquito repellents generally make up 5-30% of the final products. DEET (n, n-diethyl-m-toluamide) has been used more than any other. DEET is the compound which results from a reaction of m- toluic acid with thionyl chloride followed by a reaction with diethyl amine.

Other repellent ingredients used include citronella oil, dimethyl phthalate, lavender, lemon-grass oil, and peppermint oil. It has been found that mixtures of various repellent compounds often provide greater effectiveness than any one compound alone.

Mosquito Repellent Products
Mosquito repellents are sold as aerosols, pumps, lotions, and oils. Mosquito repellents that are sold as lotions or creams are essentially skin creams which have DEET added at a certain level.

They are primarily composed of water, surfactants, fatty alcohol, fragrance, and other emollients. When applied to the skin, these products have the dual benefit of repelling mosquitos and moisturizing skin. These products are generally less effective than aerosol forms, however, because they do not allow the active ingredients to evaporate as easily.

Mosquito Repellent Aerosols
Mosquito Repellent Aerosols ingredients:
  1. Solvent : usually used organic alcohol such as ethanol or propanol. It also used to dilute active ingredient to an appropriate concentration. It also keep all of the raw materials mixed, ensuring that the product will remain effective even after long-term storage.
  2. Propellant : The propellant is a volatile compound which creates the pressure that causes the rest of the product to be forced out of the container. Common propellants used are liquified hydrocarbon gases like propane, butane, or isobutane, hydrofluorocarbons, and dimethyl ether.
  3. Fragrances and emollients : added to make them more cosmetically appealing.
  4. Other Ingredients : ingredients to prevent corrosion and other stability problems.
The Aerosol Can
In addition to the ingredients, the packaging components are also an important part of an aerosol mosquito repellent. The can is typically a metal container made up of tin-plate steel. The coating of tin keeps the steel from reacting with the ingredients used in the repellent formulation. The valve is another key packaging component. It has the dual task of sealing the pressurized contents in the can and controlling the dispensing of these contents. Valves have three sections: a diptube, which feeds the product from the can to the valve body; the valve body, which mixes the product and propellant; and the actuator button, which when pressed, allows the product to be released.

The Manufacturing Process of Mosquito Repellent Aerosol
Compounding
  1. raw materials are mixed together in large stainless steel tanks. The alcohol is pumped into the tank, and the other materials, including DEET, fragrance, and emollients, are manually poured in and allowed to mix. All of the ingredients except the propellant are added at this phase of production. Since some of the materials in this process are flammable, special precautions are taken to prevent explosion, such as using spark-proof electrical outlets and blast-proof walls.
  2. When the batch is finished, a sample is sent to the quality control lab and tested to make sure it meets the set standards for the product. After passing these tests it is pumped to the filling lines to make the finished product. 
 Filling
  1. The filling line is a series of machines connected by a conveyor belt system that combine all of the components to make the finished mosquito repellent product. This machine has a large hopper that is filled with empty.
  2. The metal cans are automatically moved along the conveyor belt and cleaned with a jet of compressed air to remove any dust and debris. They next travel to the filling carousel. The filling carousel is made up of a series of piston filling heads that are calibrated to deliver exactly the correct amount of product into the cans. As the cans move through this section of the filling line, they are filled with product.
  3. The next step in the filling process involves topping the cans with a valve, adding the propellant, and pressurizing the cans. The valve is put on by the valve inserter machine. The valves are also put in a hopper and then correctly sorted and aligned. As the cans pass by, the valves are put on. These valves are then tightly affixed to the can by the valve crimping machine. Depending on the type of filling technique, the propellant is either injected through the valve at high pressure or injected into the can before the valve is crimped.
  4. After the cans are capped and filled, they are moved to a hot tank, a long trough filled with hot water. Here the cans are checked for escaping bubbles that would indicate a propellant leak. The high temperature of the waterbath also raises the internal pressure of the can, which is intended to cause any weak spots in the can to fail. This is a crucial quality control step that prevents damaged cans from being sold to the public.
  5. When the cans exit the waterbath, they are dried by high-pressure air jets. Other components are then added, such as the actuating button and the overcap. Any needed labels or printing are also added at this point.
  6. The finished cans are then moved to the boxing area, where they are put into boxes, typically a dozen cans at a time. These boxes are then stacked onto pallets and hauled away in large trucks to distributors. High speed aerosol production lines like the one described can move at speeds of about 200 cans per minute or more.
Quality Control Before, During and After Manufacturing
Quality control is an essential step in the production of mosquito repellents. Tests are performed at various points in the manufacturing process to ensure that the finished products are consistent from run to run, remain effective over a long period of time, and are safe to use.

Before production begins, the incoming raw materials are checked to ensure they meet the previously set specifications. Tests such as pH, specific gravity, and moisture content are typically performed. Additionally, the cans are inspected for dents, corrosion, and other weaknesses.

During manufacture, samples of the repellent are taken during different points along the filling line, and the characteristics or the product are tested. Parameters monitored :
  • level of active ingredient
  • pressure
  • spray rate
  • spray pattern.
  • ensure the cans evacuate properly.
Long-term stability studies may be done to establish that the cans do not show undue signs of corrosion.