What Is Formalin?
Formalin is an aqueous solution of the chemical compound formaldehyde. It typically contains about 40% formaldehyde by volume, and a small amount of stabilizer, usually 10% to 12% methanol. Formalin is used as a disinfectant or anti-bacterial. The formaldehyde in formalin is responsible for its disinfectant properties, while the water helps dilute it, making the solution safer to use. Methanol also helps make the solution safer, as it helps prevent oxidization and polymerization of the formaldehyde, either of which could result in fire or explosion.
Formalin is commonly used in aquariums to prevent the growth of bacterial parasites that prey on fish. It is ineffective against other types of parasites, however, including insects, larvae, and fungi. Formaldehyde kills bacteria not by poisoning them, but by dehydrating them, causing the normal fluid in the cells to coagulate, or become rigid. The formaldehyde therefore remains within the living organism rather than being expelled through the liver and kidneys as a typical toxin would be. For this reason, the amount of formaldehyde solution used in an aquarium or pond must be carefully determined to avoid dehydration of the fish.
Formalin's coagulating properties also make it ideal for use as a fixative for tissue preserved in microscopic slides. Formaldehyde can also be used topically in small quantities to dry the skin, for example in the treatment of warts. Formaldehyde treatment of warts is typically accompanies by mechanical removal of the wart, such as with an emery board or pumice stone, and may take many days. Formalin is also used as a preservative in vaccines.
Formaldehyde solutions are sometimes used in post-mortem examinations to determine whether the deceased was breathing or able to breathe at the time of death. In the so-called skin test, the lungs are removed and placed in formalin. If they float, the deceased was most likely able to breathe when he or she died.
The coagulating properties of formalin are also responsible for its common use in the past as an embalming agent. As it alters the fluid in the body cells, it not only disinfects, but also helps the structures of the body retain their shape. Cells altered by formaldehyde also help resist future bacterial infection. However, formaldehyde is no longer widely used as an embalming agent, because of health and safety concerns for living people exposed to it. Formaldehyde is not only volatile, but can be toxic, allergenic, or carcinogenic when inhaled.
Written by Niki Foster
