What is the Difference Between Formalin and Paraformaldehyde

The main difference between formalin and paraformaldehyde is that formalin is a solution of formaldehyde gas in water, often containing methanol to prevent polymerization, while paraformaldehyde is a polymerized form of formaldehyde, typically in the solid state.

Formalin and paraformaldehyde are chemical compounds commonly used in various industrial, medical, and laboratory applications.

Key Areas Covered

1. What is Formalin  
      – Definition, Features, Applications
2. What is Paraformaldehyde
      – Definition, Features, Applications 
3. Similarities Between Formalin and Paraformaldehyde
      – Outline of Common Features
4. Difference Between Formalin and Paraformaldehyde
      – Comparison of Key Differences
5. FAQ: Formalin and Paraformaldehyde
      – Frequently Asked Questions

Key Terms

Formalin, Paraformaldehyde

Difference Between Formalin and Paraformaldehyde - Comparison Summary

What is Formalin

Formalin is a solution of formaldehyde gas in water. Formaldehyde, its primary component, is a simple but highly reactive organic compound with the molecular formula CH2O. Formalin is produced by oxidizing methanol, a process often catalyzed by silver or metal oxides. This results in the formation of formaldehyde, a colorless gas with a pungent odor. To make it more practical for use, formaldehyde is dissolved in water to create formalin. The resulting solution is commonly a 37% solution of formaldehyde, with the remainder being water and methanol.

One of the key aspects of formalin chemistry is its versatility as a disinfectant and preservative. Formaldehyde is a powerful antimicrobial agent, and its ability to cross-link proteins makes it an effective preservative for biological specimens. This property is useful in medical laboratories, where formalin-fixed tissues are crucial for histopathology, allowing detailed examination of cell and tissue structures.

Formalin vs Paraformaldehyde

Figure 2: Formaldehyde

In terms of chemical reactivity, formaldehyde readily undergoes polymerization reactions. The ability of formaldehyde to form methylene bridges between molecules makes it an essential component in the production of various resins, such as urea-formaldehyde and phenol-formaldehyde resins. These resins find applications in manufacturing plywood, particleboard, and other wood products, as well as in molding processes.

Furthermore, formalin is involved in the synthesis of various chemicals. For instance, it is a precursor in the production of pentaerythritol, a compound used in the manufacture of paints, coatings, and explosives. The chemistry of formalin is also pertinent in the synthesis of certain pharmaceuticals and agrochemicals.

Despite its widespread use, formaldehyde is known to be toxic, and exposure to high concentrations can have adverse health effects. Inhaling formaldehyde vapors can irritate the eyes, nose, and throat, and prolonged exposure has been linked to respiratory and skin issues.

What is Paraformaldehyde

Composed of polymerized formaldehyde molecules, paraformaldehyde is a white, crystalline solid that depolymerizes upon heating, releasing formaldehyde gas. One of the primary reactions involving paraformaldehyde is depolymerization, which occurs when the solid is heated to about 170 degrees Celsius. This process leads to the release of formaldehyde gas, reverting paraformaldehyde back to its monomeric form. This gaseous formaldehyde is a versatile building block for various chemical reactions, making paraformaldehyde a convenient source for the controlled release of formaldehyde in synthetic applications.

In organic synthesis, paraformaldehyde is often employed as a mild and selective formylating agent. It reacts readily with amines and other nucleophiles, leading to the formation of various functionalized compounds. For example, the reaction of paraformaldehyde with a primary amine yields a corresponding N-methylolamine, which can further react to form imines or be oxidized to form amides.

Compare Formalin and Paraformaldehyde

Figure 2: Paraformaldehyde

Another notable application of paraformaldehyde is in the preparation of formaldehyde-based resins, such as phenol-formaldehyde and urea-formaldehyde resins. These resins have extensive industrial uses, including as adhesives, coatings, and molding compounds. The ability of paraformaldehyde to release formaldehyde upon heating is crucial in the crosslinking reactions that lead to the formation of these durable and versatile resins.

In biological sciences, paraformaldehyde serves as a fixative for preserving tissue specimens. When paraformaldehyde is used in conjunction with other fixatives, it helps to maintain the structural integrity of cells and tissues by crosslinking proteins. This fixation process is essential in microscopy and other analytical techniques, allowing researchers to study the morphology of biological samples.

It’s worth noting that paraformaldehyde should be handled with care due to its toxicity. Proper precautions, including the use of protective equipment and working in well-ventilated areas, are essential to ensure safe handling.

Similarities Between Formalin and Paraformaldehyde

  • They both release formaldehyde when they break down.
  • Both are useful in various industrial, medical, and laboratory applications.

Difference Between Formalin and Paraformaldehyde


Formalin is a solution of formaldehyde gas in water, often containing methanol to prevent polymerization, while paraformaldehyde is a polymerized form of formaldehyde, typically in a solid state.


While formalin is a liquid solution, paraformaldehyde is a solid.


Formalin is a solution of formaldehyde gas in water, typically containing about 37% formaldehyde, whereas paraformaldehyde is a polymer of formaldehyde consisting of repeating CH2O units and is in the form of a white powder.


Formalin is generally less stable over time, with a tendency to undergo gradual polymerization; however, paraformaldehyde is more stable and has a longer shelf life. It requires reactivation by heating to release formaldehyde when needed.

FAQ: Formalin and Paraformaldehyde

How toxic is paraformaldehyde?

Paraformaldehyde is moderately toxic by skin contact.

How do you remove paraformaldehyde?

To remove paraformaldehyde gently cover paraformaldehyde solid spills with wetted paper towels or absorbent pads to avoid raising dust and then wipe up.

What is paraformaldehyde made of?

Paraformaldehyde is made up of a polymer of formaldehyde.


Formalin is a solution of formaldehyde gas in water, serving as a versatile disinfectant and preservative. Paraformaldehyde, on the other hand, is a solid polymer of formaldehyde with applications ranging from tissue fixation to manufacturing plastics. Thus, this is the main difference between formalin and paraformaldehyde.


1. “Paraformaldehyde.” Wikipedia. Wikipedia Foundation.

Image Courtesy:

1. “Structural formula of formaldehyde” By Chem Sim 2001 – Own work (Public Domain) via Commons Wikimedia
2. “Paraformaldehyde” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia

About the Author: Hasini A

Hasini is a graduate of Applied Science with a strong background in forestry, environmental science, chemistry, and management science. She is an amateur photographer with a keen interest in exploring the wonders of nature and science.

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