Aldehydes such as formaldehyde and glutaraldehyde have wide antimicrobial properties including being sporicidal and fungicidal. However, glutaraldehyde resistance has emerged in some bacteria and it can cause health issues, leading ortho-phthalaldehyde to replace it. Formaldehyde is used as a disinfectant and biocide, including for vaccines and urinary tract infections. Glutaraldehyde is a non-volatile disinfectant preferred over formaldehyde, used in concentrations of 0.1-1.0% as a biocide and sterilant. Ortho-phthalaldehyde is commonly used to disinfect medical instruments.

1. ALDEHYDES
Aldehydes, such as formaldehyde and glutaraldehyde, have a wide microbiocidal activity and
are sporicidal and fungicidal. They are partly inactivated by organic matter and have slight
residual activity.
Some bacteria have developed resistance to glutaraldehyde, and it has been found that
glutaraldehyde can cause asthma and other health hazards; hence ortho-phthalaldehyde is
replacing glutaraldehyde.
FORMALDEHYDE
Disinfectant and biocide
An aqueous solution of formaldehyde can be useful as a disinfectant as it kills most bacteria and
fungi (including their spores). Formaldehyde solutions are applied topically in medicine to dry
the skin, such as in the treatment of warts. Many aquarists use formaldehyde as a treatment for
the parasites Ichthyophthirius multifiliis and Cryptocaryon irritans.
Formaldehyde is used to inactivate bacterial products for toxoid vaccines (vaccines that use an
inactive bacterial toxin to produce immunity). It is also used to kill unwanted viruses and
bacteria that might contaminate the vaccine during productionUrinary tract infections are also
often treated using a derivative of formaldehyde (methenamine), a method often chosen because
it prevents overuse of antibiotics and the resultant development of bacterial resistance to them. In
an acid environment, methenamine is converted in the kidneys to formaldehyde, which then has
an antibacterial effect in the urinary tract. Some topical creams, cosmetics, and personal hygiene
products contain derivatives of formaldehyde as the active ingredients that prevent the growth of
potentially harmful bacteria.
Formaldehyde is also approved for use in the manufacture of animal feeds in the US. It is an
antimicrobial agent used to maintain complete animal feeds or feed ingredients Salmonella
negative for up to 21 days.
GLUTARALDEHYDE
Disinfectant
Virtually all applications of glutaraldehyde exploit its high reactivity toward proteins. Being
nonvolatile and bifunctional, glutaraldehyde is often preferred to the less
expensive formaldehyde. It reacts with amines, amides, and thiol groups in proteins.

2. A glutaraldehyde solution of 0.1% to 1.0% concentration may be used as a biocide for system
disinfection and as a preservative for long term storage. It is a sterilant, killing endospores in
addition to many microorganisms and viruses.
Glutaraldehyde is a component of hydraulic fracturing "fracking" fluid. It is included in the
additive called Alpha 1427, as a biocide.[13]Bacterial growth can impair the production of oil and
gas wells, and can be introduced into the formation from various sources including the source
water, proppant, and polymers used in the hydraulic fracturing process. Glutaraldehyde is
pumped as a liquid additive with the fracturing fluid to reduce or eliminate this source of
formation and fracture conductivity damage.
OPA
Disinfection
OPA is commonly used as a high-level disinfectant for medical instruments. Disinfection with
OPA is indicated for semi-critical instruments that come into contact with mucous membranes or
broken skin, such as specula, laryngeal mirrors, and internal ultrasound probes