Formalins

Formalin is an aqueous solution of formaldehyde gas in water, commonly used as a preservative, fixative, and disinfectant in biology and medicine. The term typically refers to formaldehyde solutions stabilized with methanol. In laboratory practice, several formulations are used. A widely employed fixative is 10% neutral buffered formalin (NBF), which contains about 3.7–4% formaldehyde in water buffered to neutral pH (around 7.0). The stabilizer methanol helps prevent polymerization of formaldehyde in solution. A stock solution of approximately 37% formaldehyde in water is also common, but is usually diluted for routine use.

Common uses include fixation of biological tissues for histology and pathology, preservation of specimens for study, embalming, and surface disinfection of equipment or work areas. Fixation with formalin preserves cellular and tissue structure by crosslinking proteins and nucleic acids, forming methylene bridges that stabilize morphology and slow enzymatic degradation. The exact outcome depends on concentration, temperature, duration, and subsequent processing.

Safety and handling require caution. Formaldehyde is volatile, irritant to eyes, skin, and the respiratory tract, and is classified as a known human carcinogen by many health authorities. Adequate ventilation, fume hoods, and appropriate personal protective equipment are recommended. Methanol used as a stabilizer adds its own toxicity. Spills should be managed with proper cleanup procedures, and waste must be handled as hazardous chemical waste in accordance with local regulations. Storage should be in tightly closed containers, protected from heat and direct light.

Formalin remains a foundational chemical in laboratory preservation and histology, valued for its effectiveness in maintaining tissue architecture while requiring careful safety practices.