In physicochemical terms, an aerosol is a colloid state in which very fine particles of a solid or liquid are dispersed in a gas.

The insecticides and hairspray first developed are aerosols in the original sense but the word aerosol is also applied as a blanket term to any product in which a liquid or solid is discharged from a pressure-resistant container using the pressure of a gas. As they are very functional, aerosols are widely used for cosmetics.

Aerosol products are classified as follows according to the form of the contents when they are discharged from the container:

1. Mist-form products like hairspray, etc.
2. Powder-form products like powder spray, etc.
3. Foam-form products like hairstyling foam, etc.
4. Paste-form products like creams, etc.

Cosmetics products frequently use mist and foam forms.

What are aerosol manufacturing methods in cosmetics?
Before going to mass production, it is necessary to carry out various production trials to make thorough checks on such items as product stability, container corrosion, and gas permeability.

Manufacturing Process
Below is a step by stem process guideline:

1. In leakage inspection, all products are checked for gas leaks by placing them in hot water at 55 degrees Celsius for 2-3 minutes.
2. In the discharge inspection, the aerosol is discharged for several seconds as required.
3. The internal pressure and inflammability testing are carried out by the regulations.

When aerosols are mass-produced, complaints may arise due to variations in production so it is necessary to have them as uniform as possible to ensure product quality.

Filling methods for propellant gas
The filling methods are cold filling and pressure filling. There are two types of pressure filling: under-Cup filling and through the valve filling.

1. Cold Filling: The concentrate and gas are cooled before filling, the gas being liquefied beforehand. This method is not used much nowadays.
2. Under-Cup pressure filling: After putting the concentrate in the container and inserting the valve, removing the air through the gap between the valve and the container, the gas is put in and the valve is crimped in place. This method is used for such products as hairspray which contains a lot of gas.
3. Through-the-valve pressure filling: After putting the concentrate in the container, removing the air, and crimping the valve, the gas is injected under pressure through the orifice in the valve through which the aerosol contents come out. This is a very accurate filling method and is used for foam-form products which use small amounts of gas.

What precautions should we take when using aerosol cosmetics?
To ensure the safe use of aerosol cosmetics, attention should be paid to the following points:

1. Cautions regarding pressure: It is dangerous t use aerosol products at temperatures above 40 degrees Celsius because the pressure increases. Low temperatures cause the internal pressure to drop making it difficult for the product to be discharged properly.
2. Inflammability Cautions: As they use inflammable gases and inflammable ingredients are much used in their concentrates, aerosols must not be used near naked flames. Aerosols must not be incinerated because they could explode.
3. Disposal Cautions: Aerosols must only be discharged by the displayed cautions for this. Any gases remaining could cause fires in the garbage when in the garbage truck or other places.
4. Usage Cautions: The displayed method of use must be observed. Products on the market comprise those which are used upright, those which are used inverted, and those which are used in all attitudes. Non-observance of the displayed method of use may cause the gas to escape rendering the aerosol unusable.

What are some recent developments in aerosol technology?
Due to their convenience, the use of aerosol cosmetics has been increasing in recent years. The following describes special types of containers that have been developed for them.

1. Special aerosol containers: Special aerosol containers comprise different types of the compartment can use either an inner bad or piston system.
2. Inner bag system: This type of compartment has a soft inner bag (made from PE or soft aluminum) which is filled with the aerosol contents while the outer part of the container is filled with gas. The pressure of the gas squeezes the inner bag causing the aerosol contents to be discharged.
3. Piston System: In this type, there is a piston inside the container. The part of the container above the piston is filled with the aerosol contents and that below it with gas, the pressure of which pushes up the piston valve discharging the contents from the container.
   These types of double containers have it possible to make high viscosity concentrates into commercial aerosol products and are also good for aerosols in which the concentrate should be discharged by itself as the concentrate and gas are separated inside the container.
4. Making aerosols environment friendly: When designing aerosol products, it is necessary to consider such environmental aspects as their effect on the ozone layer, atmospheric pollution, and global warming. With this in mind, positive efforts are now being made to reduce the amount of gas used and develop containers that use no gas at all.

As examples of the latter, several manual atomizers, electric sprayers, compressed air, and other systems for mist-form products, and in the case of liquid-form products, dispensers, and systems that discharge the concentrate as foam are being developed. ​​​​​​​