What Is Formalin?

Before moving into a new home, formaldehyde solution (formalin) is sometimes used. But what exactly is formalin?

What Is Formalin?

Formalin is an aqueous solution of formaldehyde. It appears as a colorless, transparent liquid with strong corrosive properties and high volatility. It emits a pungent, irritating odor that may irritate the conjunctiva and cornea of the eyes or strongly stimulate the respiratory system. Commercial formalin typically contains approximately 35–40% formaldehyde by weight and possesses preservative, disinfectant, and bleaching properties. Its applications vary across different fields. In medicine, for example, formaldehyde can coagulate proteins and is therefore widely used as a tissue fixative and preservative in laboratory settings. When a small skin tumor is surgically excised, it is often placed into a specialized specimen bag and immersed in a small amount of liquid—commonly formalin—as instructed by the physician for transport to the pathology laboratory. This liquid serves to fix the tissue, enabling subsequent histopathological sectioning and microscopic examination.

The applications of formalin are extensive. When used at appropriate concentrations and dosages, it effectively kills most microorganisms and is thus commonly employed as a disinfectant. Industrially, formalin has numerous uses—for instance, in the production of adhesives, dyes, paints, and resins—and is frequently encountered in everyday life.

Formalin should be stored in tightly sealed, amber-colored glass bottles—not in metal containers—and kept in a cool, stable-temperature environment to prevent precipitation of white, flocculent paraformaldehyde.