Phenolic compounds used as antiseptics or disinfectants include pure phenol and substitution products with halogens and alkyl groups. They act to denature proteins and are general protoplasmic poisons.

Phenol (carbolic acid) is bacteriostatic at concentrations of 0.1–1% and is bactericidal/fungicidal at 1–2%. A 5% solution kills anthrax spores in 48 hr. The bactericidal activity is enhanced by ethylenediamine tetraacetic acid (EDTA) and warm temperatures; it is decreased by alkaline medium (through ionization), lipids, soaps, and cold temperatures. Concentrations >0.5% exert a local anesthetic effect, whereas a 5% solution is strongly irritating and corrosive to tissues. Oral ingestion or extensive application to skin can cause systemic toxicity, manifested primarily by CNS and cardiovascular effects; death may result.

Phenol has good penetrating power into organic matter and is mainly used for disinfection of equipment or organic materials that are to be destroyed (eg, infected food and excreta). Because of its irritant and corrosive properties and potential systemic toxicity, it is not used much as an antiseptic except to cauterize infected areas, eg, infected umbilicus of neonates. It is also incorporated into cutaneous applications for pruritus, stings, bites, burns, etc, because of its local anesthetic and antibacterial properties to relieve itching and control infections.

Cresol (cresylic acid) is a mixture of ortho-, meta-, and paracresols and their isomers. It is a colorless liquid; however, after exposure to light and air, it turns pink, then yellowish, and finally dark brown. A 2% solution of either pure or saponated cresol “lysol” in hot water is commonly used as a disinfectant for inanimate objects.

Hexachlorophene has a strong bacteriostatic action against many gram-positive organisms (including staphylococci) but only a few gram-negative ones. It is used widely in medicated soaps. Frequent washings every day with hexachlorophene soaps lead to sufficient retention of residue on the skin to provide prolonged bacteriostatic action. Washing with other soaps promptly removes these residues. Repeated exposure of skin to high concentrations of hexachlorophene may lead to sufficient absorption of the antiseptic to cause spongiform degeneration of the white matter in the brain and cause nervous disorders. To prevent such neurotoxicity, products containing >0.75% hexachlorophene are available only by prescription. Accidental oral ingestion of hexachlorophene results in acute poisoning.

Pine tar is a viscid blackish brown liquid, used primarily for antiseptic bandaging of wounds of the hoof and horn. Pine tar contains phenol derivatives that provide antimicrobial properties.

Chloroxylenols are broad-spectrum bactericides with more activity against gram-positive than gram-negative bacteria. They are active in alkaline pH; however, contact with organic matter diminishes their activity. Streptococci are more susceptible than staphylococci. Parachloro-metaxylenol (PCMX) and dichlorometaxylenol (DCMX) are the 2 most commonly used members of this group. DCMX is more active than PCMX. Strong solutions of these compounds can cause irritation and have a disagreeable odor. A 5% chloroxylenol (eg, PCMX) solution (in α-terpineol, soap, alcohol, and water) is diluted with water (1:4) for skin sterilization and (1:25 to 1:50) for wound cleansing and irrigation of the uterus and vagina. PCMX is also combined with hexachlorophene to enhance its antibacterial spectrum and to prevent contamination by gram-negative organisms.

Last full review/revision March 2012 by Mark L. Wickstrom, DVM, MS, PhD