Preservative: What is a Preservative? How does preservative work? How to choose a preservative? 7 BEST FAQ for beginners

October 30, 2020

What are preservatives?

Preservatives are used to keep a product shelf stable for a longer period of time than it would by itself. They are also put in products to prevent the growth of harmful molds, fungi, and bacteria that would occur without them.

However, food is not the only thing that needs preservatives. Cosmetic products need preservatives too! Without them, bacteria would be transferred from the skin back into the container via application brushes or the fingers, where it could multiply unobstructed.

The one seemingly obvious solution is to just make products that are extremely acidic or extremely alkaline (basic) to prevent bacterial growth, but this would result in damage to the skin, which is very sensitive to pH changes.

Bacteria in petridish

What kinds of preservatives are there?

There are many different kinds of preservatives. These include aldehydes, glycol ethers, isothiazolinones, organic acids, and parabens.


Aldehydes are carbon-based compounds that contain an aldehyde group (a carbon double-bonded to oxygen and single-bonded to a hydrogen). This group includes formaldehyde, which is notorious for the smell it produces in laboratories and hospitals, and formaldehyde producing compounds.

They are very effective antimicrobials as they react with proteins and peptides, destroying them and preventing the bacteria from replicating. However, formaldehydes and products that decompose into formaldehyde are extremely dangerous to human health.


Glycol ethers are a group of ethers that have a glycol base and an ether functional group.

They include phenoxyethanol and caprylyl glycol. A glycol is an alcohol with two hydroxyl groups, also known as a diol. An ether functional group is a carbon with a hydroxyl group and an oxygen double bonded to it.

They are soluble in oils and water. They are very effective against gram-negative bacteria. While they are not broad-spectrum, they are considered a milder and less irritating alternative to other preservatives.


Isothiazolinones are five-sided rings, one side of which has a carbon/carbon double bond. One point on the ring is a sulfur, another is a nitrogen, and one carbon that is double-bonded to oxygen. They are broad-spectrum preservatives and have the bonus of being effective in the full range of pH values.

Organic acids are simply organic or carbon based compounds with acidic properties.

These include acetic acid, lactic acid, anisic acid, and benzoic acid as well as the sorbates. They are sometimes considered natural despite being created synthetically. In products with high water content, they precipitate out and lose their effectiveness. While they are strong against fungi, they do not have much of an effect against bacteria.


Parabens are a form of hydroxybenzoate attached to an alkyl (chain of single-bonded carbons) group. They have bactericidal and fungicidal properties and are used in foods, cosmetics, and pharmaceuticals. These are the most common preservatives found in cosmetics.

They are permitted for use in leave on and rinse off products. However, there is also a controversy over their effects on human health.


Parfum is another ” Natural Preservative” system used by natural skin care brands.

Do not confuse Parfum with Perfume which is fragrance.

Parfum is not a single compound but a mixture of dozens of them. It is a broad spectrum preservative that is soluble in water, alcohols, and glycols. While it smells nice, it is very expensive.

Do read more on Parfum here


Some antioxidants are often touted as preservatives. While they have less intimidating and more ‘natural’ names, they will not accomplish the job. Antioxidants are not preservatives. These are sodium lactate, grapefruit seed extract, rosemary antioxidant, and vitamin E.

What are some preservatives in each of these categories?

The aldehydes include Germall Plus, DMDM, Imidazolidinyl Urea, and Diazolidinyl Urea. The glycol ethers include phenoxyethanol, Optiphen, and Optiphen II. Isothiazolones include Kathon.

Organic acids include Geogard, Neodefend, Euxyl, sodium benzoate, potassium sorbate, anisic acid, and levulinic acid.

Parabens include Germaben II, Methylparaben, Propylparben, and Butylparben, and Pheonip.

Are they safe?

The FDA does not have any regulations for cosmetic products. Instead, it is the burden of the manufacturer to ensure that the ingredients are safe. However, there are laws that require product labels to show what they contain.

Parabens are one of the most controversial of the preservatives and often a topic to debate on with many skincare formulators. There are very contrasting studies about this preservative. I would suggest to do your own research about this preservative.

To start with here are few link that I think will be useful to start your own research

One alternative that has been tried is phenoxyethanol. However, it has its own health concerns. It has the potential to cause an allergic reaction. Ingestion of phenoxyethanol can result in vomiting, diarrhea, and respiratory irritation.

Formaldehydes and preservatives that decompose into formaldehyde are hazardous to human health. It is a known carcinogen and can also cause contact dermatitis, even in short term use.

Quaternium 15, a common preservative in many cosmetics, decomposes into amounts of formaldehyde that are small enough to be considered safe. However, this has not shown to be beneficial in any way. Many cosmetics companies are phasing out this dangerous class of preservatives.

Do I need preservatives in my DIY skincare?

Preservatives are not required in any homemade products. However, if you plan to sell them, some kind of preservative should be included to prevent spoilage.

If you do not add a preservative to your formulation, treat it as you would a fresh fruit or vegetable by putting it in a refrigerator to prevent fungi and bacteria growth.

Products that are not water based do not normally need preservatives.

How much of X preservative do I need?

This varies based on the product and the preservative. Typical usage rates are .5% to 2.5% by mass. If you have 100g of other ingredients, then 1% usage rate means you add one gram to the mixture.

Which preservative should I use?

There are too many preservatives to choose from, but no table or website can tell you

which one to use. Instead, do your own research. Take into account the product you’re putting it in. Is it oil-based? Water-based? What pH will it have? Are any of the other ingredients preservatives too? Are you willing to use multiple preservatives? Is cost a factor? All of these can change which preservative is best for your recipe.

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    Dr. Namrata yadav
    November 6, 2020 at 1:51 pm

    Very nice and comprehensive

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    June 27, 2021 at 8:38 pm

    Such amazing information! Thank you very much and wish to see more write ups from you! Love your recipes too

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