Synthetic Preservatives

Here are some of the most commonly used synthetic preservatives for both personal care and for cleaning products used throughout the home.

Benzalkonium Chloride: This quaternary compound is primarily active against gram-positive and some gram-negatives, and has a recommended usage concentration of 0.1 to 0.3%. Soluble in both water and alcohol, benzalkonium chloride has an optimum pH level of between 4 and 10.

Benzyl Alcohol: Often used to relieve itching, particularly in cosmetic eye products, benzyl alcohol is also used as a local anesthetic and as a rather effective bacteriostatic agent. Water soluble at 1g/30ml, a concentration of 1 to 3% is recommended for preservative use.

Bronopol: Bronopol, or scientifically, 2-bromo-2-nitropropane-1, 3-diol, is an effective synthetic preservative but with only minimal activity against yeast. The water soluble bronopol is stable in acidic environments with an optimum pH level of 6. Although it hasn't been a widely used preservative in the United States due its pH sensitivity and its tendency to impart color changes in products, it is used commonly in other countries outside of the U.S.

Chlorhexidine Gluconate: This cationic compound is unstable at higher temperatures and has limited usage but is most effective against bacteria.

Incompatible with many gums and anionics, the optimal stability of chlorhexidine gluconate's pH level is neutral, but the preservative remains active between 5 and 8, with the recommended usage levels between 0.01 and 0.1%.

Chloroxylenol: Chloroxylenol, or Ottasept, is soluble in alcohol, poorly soluble in water, and tolerates a wide range of pH levels. The recommended usage concentrations of this halogenated phenolic compound that features both antifungal and antibacterial properties is 0.2 to 0.8%.

Dehydroacetic Acid: A bacteriostat and also fungistat, dehydroacetic acid is a water soluble preservative that's effective within a pH range of 5 to 6.

Diazolidinyl Urea: Belonging to the Germall family of synthetic preservatives, diazolidinyl urea is predominantly effective against bacteria that is gram-negative and is also used as a formaldehyde donor. This water soluble preservative performs best between a pH level of 3 to 9, with recommended usage concentrations between 0.03 and 0.3%.

DMDM Hydantoin: Also called Glydant, water soluble DMDM hydantoin is a synthetic preservative that's the least effective against yeast, and has an optimal pH level of between 4.5 and 9.5.

Ethyl Alcohol: 15 to 20% is the recommended concentration of ethyl alcohol which is effective for protection against fungi and bacteria.

Formaldehyde: This effective synthetic preservative is useful for protecting against a broad range of fungi and bacterium, although it becomes inactive when exposed to certain proteins, gelatins in particular. Formaldehyde isn't often used as a preservative due to adverse reactions in some people, but it is still present in some products that are used and quickly rinsed off. The optimal pH level is between 3 and 10, with concentration usage ranging from 0.05 to 0.2%.

Glutral: Also called Ucarcide, glutral is a water soluble synthetic preservative that has the ability to remain active throughout a wide pH range. Chemically a glutaraldehyde, usage concentrations of glutral range from 0.02 to 0.2% of a 50% solution, and is considered to be a broad spectrum preservative.

Imidazolidinyl Urea: This water soluble preservative features a wide pH tolerance, and when combined with parabens, offers a broad spectrum of antimicrobial activity. However, the usage of this synthetic substance is restricted as it yields low levels of the preservative formaldehyde.

Kathon CG: Kathon CG, otherwise known as methyl, chloromethyl isothiazolinone and methyl isothiazolinone, are all synthetic materials used to create a preservative that actively protects against fungi, bacteria, and yeast. Available in an aqueous solution, consumers should contact the individual manufacturer for exact usage concentrations regarding this preservative that's primarily designed for use in products that are rinsed off, such as body washes or hair care products. Kathon CG is able to tolerate the entire pH range.

Liquapar: Liquapar is a mixture of isopropyl parabens, isobutyl, and N-butyl and is most effective against mold, yeast, and some bacterium. Able to tolerate a wide pH range, the typical usage level for liquapar is 0.5 to 0.3%.

Parabens: Parabens are the combination of several esters of methyl, ethyl, propyl, and butyl, or benzoic acid and has been widely used to protect against both fungi and gram-positive bacteria, although it tests poorly for use against pseudomonas. The optimal pH level is 8, but it remains effective over a wide range and can be complemented with other preservatives that are effective against gram-negative microorganisms.

Phenoxyethanol: This synthetic preservative is a phenolic derivative that's mainly effectively against gram-negative bacteria and features a wide range of pH tolerance. .

Both water and alcohol miscible, the recommended usage concentrations of phenoxyethanol is between 0.5 and 2%

Phenyl Ethyl Alcohol: Active mostly against gram-negative bacterium, phenyl ethyl alcohol features a rather pleasant floral aroma and is water soluble up to two percent.

Phenyl Mercuric Acetate: Used in cosmetics, especially products used on the eye such as mascara, phenyl mercuric acetate is used for protection against fungi and bacterium. Useful where other preservatives have failed, phenyl mercuric acetate is soluble in hot ethanol, but poorly soluble in water. When used as a preservative, the concentrations range from 0.002 to 0.125%.

Potassium Sorbate: Generally active against yeast and mold, the water soluble potassium sorbate has an optimal pH level of anything up to 6.5.

Quaternium 15: Also known as Dowicil 200, quaternium is a widely effective water soluble preservative with an equally wide pH range of 4 to 10.

Salicylic Acid: Effective for protecting against fungi and bacteria, salicylic acid will cause a discoloration in products containing iron, and is poorly water soluble. In the highest concentrations, this preservative is used in cosmetics as a keratolytic, with optimal pH levels between 4 and 6, and a usage concentration of 0.1 to 0.5%.

Sodium Benzoate: Sodium benzoate, which is benzoic acid and its salts, has widely been used in the food industry as a preservative and is active against yeast, some molds and bacterium. Sodium benzoate is water soluble and has a recommended usage concentration of 0.1 to 0.2%.

Sorbic Acid: Sorbic acid is commonly used in foods such as cheese as an antifungal agent, and inhibits the growth of yeast and mold. Soluble in alcohol and slightly in water, sorbic acid becomes inactive above a pH level of 6.2, with the optimal range being 2.5 to 6. Usage concentrations range from 0.10 to 0.30%.

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