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The Eye-Opening Truth About Preservatives In Hair Products

September 26, 2022


Verna Meachum

mage showing hair product with bacteria developing

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Curl care

With extensive experience in the beauty industry, I specialize in writing for curly hair care brands, websites, and magazines.

Not only do I have curly hair, but my children, friends, family members, and even friends who are professional curly hairstylists, each with their unique curly textures.

 You get the point :) 

I also partner with a friend who holds a Ph.D. in chemistry and works as an R&D Chemist, ensuring our content is scientifically accurate and help us navigate through the misinformation around curly hair care. 

Hi,I'm Verna

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Last Updated on April 9, 2023 by Verna Meachum

Being a conscious consumer is important to you, and you’re getting better at critically evaluating labels and perhaps, making sure that what you put in your body is healthy too.

Nonetheless, you always think about what will make your curls more manageable and healthy.

When it comes to spending money on curly hair products, there is a lot of information to sort through.

You want the most up-to-date and good-for-your-hair ingredients, but how long will the shelf life of your favorite hair mask be before it goes bad?

You don’t have to be a chemist to understand the importance of preservatives in hair products. We all know that without them, hair products would quickly become contaminated and unsafe to use.

In this article, we will discuss:

– What preservatives are

– The role of preservatives in a formula

– Types of preservatives

– The required amount of preservatives for each batch

– If all preservatives are bad

– And finally, what natural preservative are for hair products

What Are Preservatives In Hair Products?

Cosmetic products are vulnerable to microbial contamination, and they need a preservation system to inhibit microbial activity.

Preservatives are the chemical compounds added in the formulation to preserve its physical and chemical properties. This can be either while the product is stored in a warehouse or when it is being used by consumers.

A preservative molecule could be synthetic man-made or naturally derived. The fact is all products whether organic, natural, vegan, or just a simple shampoo, must have a preservation system in place to maintain the product quality.

Typically, a given product may contain 1-2 preservatives blended to enhance shelf life and extend a good shelf-life. 1

Microbes and Microbial Activity: Why do we need preservatives?

Microscope view of bacteria flowing.

Microbes are microorganisms, living creatures just like humans and other animals or plants. They exist in great numbers all around us.

Truth be told, microbes are practically everywhere and they have a way their own living system. Among them, bacteria and fungi are two of the most frequently dealt with in cosmetics. 2-4

Microbes (both bacteria and fungi) trigger undesired biochemical changes in a formulation e.g.

·      The product may change its color

·      Mal-odor – product may smell bad like rotten food

·      Black, darkened particles, or spots may appear

The three above are visible changes that customers may notice, and they are typical indications of bacterial contamination.

Using a contaminated product on the skin or hair may cause serious problems. For example:

·      Redness on scalp or skin

·      Allergy

·      Eczema

·      Serious dermatitis

Adding preservatives helps to stop the growth of microbes and makes the finished product last longer.

Where do they come from?

Microbes are everywhere. Their pores (like seeds) are present in the air, and water, and can even survive on hard surfaces.

Water is the main source of microbial contamination. Microbes, just like other living organisms, require two essential substances to live and grow their colonies.

·      Water

·      Oxygen

Water activity is the main aspect of microbial growth. Controlling the quality of water used in the formulation can inhibit microbial activity.

Moreover, these microorganisms grow more rapidly in formulations comprising a high dosage of natural ingredients e.g proteins, sugar or starch-based ingredients, and herbal or natural floral extracts.3

The Role of Preservative in a Formulation

Preservatives are chemical agents having a strong anti-microbial effect. Their chemical structure disrupts the microbial life cycle.

The exact mechanism of action is different for each preservative. A common observation is that preservative molecule attacks the cellular structure of bacteria or fungi.

This disturbs their inner cellular organs, DNA, and mitochondrial activity and disturbs their enzymatic balance. This unsettles their reproduction and thus inhibits their growth.

In fact, with some preservatives, microbial cells may eventually die, inhibiting their normal-growth cycle and controlling their population in the formulation.

Commonly used preservatives in hair care products:

·      Alcohols: Benzyl Alcohol, Phenol, Isopropyl Alcohol

·      Benzoic acid, Sodium Benzoate

·      Sorbic acid, Potassium Sorbate

·      Parabens

·      DMDM Hydantoin

·      Phenoxyethanol

·      Methylchloroisothiazolinone and Methylisothiazolinone

·      Imdazolidinyl Urea & Diazolidinyl Urea

·      Caprylyl Glycol

What is the required amount of preservatives for each batch? What effect does concentration have?

Each preservative molecule has a slightly different chemistry, solubility, and compatibility with other ingredients present in the formulation.

In technical terms, each preservative molecule has a minimum inhibitory concentration (MIC value), which is determined experimentally using a microbiological protocol. MIC is the minimum amount of a preservative that is effective to inhibit the growth of certain microbes.

Scientific literature and regulatory bodies have defined the MIC values for each preservative and formulators are required to follow these instructions in a given formulation.4

It needs to be noted that, generally one single preservative may be highly effective against bacteria, however, may not be effective against fungi.

It is practically difficult that a given preservative is highly effective against a wide range of microbes. That’s why it is normal to have a blended mixture of 1-2 (or, even 3) preservatives to have an effective wide-spectrum protection against all possible types of microbes.

Certain ingredients are multifunctional and have various tasks to play depending upon, how they are used and how much they are used.

For example, isopropyl alcohol (IPA) is a common disinfectant having an excellent inhibitory profile against bacteria and fungi (even against viruses as it is often used in hand sanitizers).

The same IPA can be used as a cosmetic preservative in small concentrations. At its minimum inhibitory concentration level, it effectively inhibits the growth of microbes and preserves the formulation.

Interestingly, at a low concentration level, IPA may not pose any adverse impact or drying effects on skin or hair fibers.

Consumer Friendly Preservatives: New Trends

Over the years, scientific research have improved our understanding of the significance of preservative chemicals and the potential hazard to consumer health.

Various skin compatibility studies and toxicological investigations (both in vitro and vivo) have made it possible to screen most of the preservatives and enlist consumer-friendly preservatives.

Based on recent studies and market trends, the following main points are enlisted here as guidelines:

✖︎  Avoid hair care formulations containing Parabens. They are still allowed in most countries; however, they may be susceptible to carcinogens.

✖︎  Formaldehyde-releasing preservatives: should be avoided, potential carcinogenic and skin irritant causes breathing discomfort.

✖︎  Formaldehyde itself (also known as Formal & methylene glycol).

✖︎ DMDM-Hydantoin – another commonly used formaldehyde-releasing molecule.

✖︎  Imdazolidinyl Urea & Diazolidinyl Urea – both releases formaldehyde in water.

✖︎  Methylchloroisothiazolinone and Methylisothiazolinone – avoid this mixture, its a skin irritant and potentially causes strong skin allergic reaction to sensitive and infant skin.

Natural Preservatives

Image of natural preservatives in hair products; plant extracts, herbs, essential oil

Consumers groups and regulatory bodies are increasing pressure to seek green and sustainable solutions for cosmetics products.5-6 In that regard, preservatives are the key players.

Scientists have developed new preservation technology and have made it possible to preserve hair care formulation using more nature-sourced and biodegradable ingredients:

✔︎  Benzoic acid and Sorbic acid and their salts – are a time tested preservatives having good biodegradation.

✔︎  Musa sapientum (Banana) Leaf/Trunk Extract with good preservation profile for hair rinse-off and leave-in formulations.

✔︎  Herbal blend: Wasabia Japonica (wasabi) root extract, Zingiber Officinale (ginger) root extract, Allium Sativum (garlic) bulb extract.

✔︎  Lonicera Caprifolium (honeysuckle) flower extract.


Keeping your hair care products fresh and bacteria-free is essential, which is why preservatives are key.

While there are many different types of preservatives, each with their own benefits and drawbacks.

The perfect preservative shouldn’t cause any allergic reactions to the skin and hair, and should extend the shelf-life of a product.

More natural, green solutions are available today, and consumers, as well as formulators, are seeking these new alternates for skin-friendly solutions.


1. Brannan, D. K., Cosmetic preservation. J. Soc. Cosmet. Chem. 1995, 46 (4), 199-220.
2. Mitsui, T., Preservation of cosmetics. In New cosmetic science, Elsevier: 1997.
3. Roden, K., Preservatives in personal care products. Microbiology Australia 2010, 31 (4), 195-197.
4. Steinberg, D. C., Preservatives for Cosmetics. Allured Publishing Corporation: 1996.
5. Papageorgiou, S.; Varvaresou, A.; Tsirivas, E.; Demetzos, C., New alternatives to cosmetics preservation. J. Cosmet. Sci. 2010, 61 (2), 107.
6. Weber, K., New alternatives to paraben-based preservative blends. Cosmetics and toiletries 2005, 120 (1), 57-62.


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