Difference Between Formalin and Formaldehyde

Formalin vs Formaldehyde

Chemically, both formalin and formaldehyde refer to the same active compound, but they differ in the formulation. Formaldehyde acts as the basic chemical, but its name has attracted many synonyms to follow. Starting from its chemical systematic name which is ‘methanal’, it is also known as; Formalin, Formic Aldehyde, Paraform, Formol, Fyde, Formalith, Methylene Glycol, Methyl Aldehyde, Methylene Oxide, Oxomethane etc. Most of these terms are commonly used commercially to represent slightly different formaldehyde formulations.


Formaldehyde is a simple, organic, chemical compound that belongs to the functional group called ‘aldehydes’, hence the suffix. It is also the simplest form of the aldehyde present with the chemical formula CH2O or HCHO and is in gaseous state at room temperature. Formaldehyde gas is colourless and has a characteristic odour with a pungent nature.

Formaldehyde is industrially produced through the catalytic oxidation of methanol (CH3OH). Silver catalysts are generally used in this process. Being a simple organic compound, formaldehyde makes way as a starting material in a tremendous amount of organic reactions. It is also used in many industrially important polymerization reactions such as urea-formaldehyde resin, phenol-formaldehyde resin etc. Formaldehyde is also used in the production of varieties of plastics, fabric crease-resistants in the textile industry, component material for automobile engine systems etc. Dilute solutions of formaldehyde are also used as disinfectants and to preserve biological specimens. As mentioned above, formaldehyde shows a complicated nature as it adopts many different forms either by cyclization, polymerization or dissolution; however, it continues to show the same chemical characteristics as formaldehyde. Given all the benefits though, formaldehyde is known to be a human carcinogen and, in fact, is toxic to all animals as exposure to formaldehyde can cause serious health issues. Furthermore, solutions of formaldehyde show highly corrosive nature and formaldehyde can form extremely volatile/explosive compounds.


When dissolved in water, formaldehyde undergoes hydration and forms the hydrate ‘Methanediol’ [CH2(OH)2] and exists in equilibrium with other forms of formaldehyde polymer. A saturated water solution containing 40% of formaldehyde by volume or 37% formaldehyde by mass is called pure formalin or 100% formalin. A typical commercial grade formalin solution would also have about 10-12% of methanol and metallic compounds. These act as stabilizers and prevent the oxidation and polymerization of formaldehyde within the formalin solution preserving its activity. If stabilizers are not added, formaldehyde aqueous solutions are highly unstable and would polymerize into large molecules that are insoluble and would precipitate out of solution.

During the production of formaldehyde from methanol, water is also produced as a by-product; hence the process can produce formalin directly when correct concentrations are reached. Formalin is generally used to preserve animal and tissue specimens and more dilute solutions are used as antibacterial washes & disinfectants, i.e. to disinfect aquariums. Formalin also has an irritating smell similar to formaldehyde. Furthermore, it possess similar toxic properties of formaldehyde as formalin readily releases formaldehyde gas and is also highly flammable.

What is the difference between Formalin and Formaldehyde?

• Formaldehyde is a basic chemical compound whereas formalin is a formulation of formaldehyde in aqueous solution.

• Formaldehyde is a gas at room temperature, but formalin is in liquid form.

• Formaldehyde is an aldehyde whereas, in formalin, formaldehyde is hydrated into an alcohol compound.

• Formalin is mainly used as a disinfectant, but formaldehyde is an essential material in many vital industrial processes responsible for producing important products.