3) INGREDIENTS - preservatives, emulsifiers & emollients

2) COSMETIC INGREDIENTS

Ideally, cosmetics should be microbiome-friendly, meaning that they have either a neutral or positive effect on microbiome health.

Important formulation challenges to consider include the acidity of the product, as well as the presence of potentially damaging ingredients, such as some surfactants and preservatives. A well balanced cosmetic product with appropriate fats and waxes can become a beneficial nutrient source for the skin microbiome, helping to combat dehydration, inflammation, itching and aging amongst other things.

The skin’s natural pH sits between approximately 4 - 6.⁴ Rinse-off cosmetics (such as soaps and shower gels) tend to be neutral or alkaline (a pH of 7 or above), so they can disrupt the natural pH. Products with a more acidic (lower) pH than 5.4-5.9 are less likely to cause dysbiosis than products with a higher pH.¹

Rinse-off cosmetics generally contain surfactants which can damage lipids and proteins in the stratum corneum. Some surfactant deposits can remain on the skin for weeks, reducing barrier protection and disrupting microbes.¹

2.1) Preservatives

2.1a) Why do we need preservatives?

Water is a substrate for microbial growth, so preservatives are particularly important in water-based products to prevent contamination.

2.1b) What do we know about their safety?

Preservatives must meet certain safety standards for cosmetic use. They cannot overtly seriously harm or kill you. Formaldehyde is an excellent preservative — hence its use in embalming — but it is extremely toxic. Adding it to your lipstick range would land you in considerable trouble. But there are no laws that specifically prohibit preservatives for disrupting your microbiome.

Many preservatives have been shown to have detrimental impacts on skin health, for example:

• Preservatives can be more effective at killing beneficial skin bacteria than pathogens.⁵ Common cosmetic preservatives (such as methylparabens) kill two of the main skin commensals, Cutibacterium acnes and Staphylococcus epidermidis.^1,5
  

• Preservatives may remain deposited on the skin even after repeated washing, causing dysbiosis.¹

Some research shows that preservative-free formulations can be beneficial to the skin. A study in the journal Microorganisms (2024)⁵ examined the effects of skincare with and without preservatives in a ‘split-face’ double-blind study. After three weeks the preservative free formulation resulted in fewer wrinkles, less redness, and greater microbial diversity. The authors found that the presence of preservatives resulted in lower levels of Neisseria and Sphingomonas (both known to benefit skin health).

Decreased levels of Neisseria are associated with:⁵

• Trans-epidermal water loss (dehydration)

• Loss of firmness and elasticity

• Increased oiliness, wrinkles and redness

Interestingly, going to bed late reduces levels of Neisseria. Early nights may be an anti-aging tool.

Decreased levels of Sphingomonas are associated with:⁵

• Aging

• Cellular senescence

• Increased vulnerability to UV damage

• Increased reactive oxygen species in keratinocytes

Beyond skin effects, preservatives may be negatively impacting our hormones, the environment, and the effectiveness of antibiotics against serious infections.

Though the extent of the impact is unclear, parabens, petrolatum and phthalates have all been demonstrated to disrupt hormones.⁹ Parabens exhibit weak oestrogen-like activity and a link between parabens deposited in breast tissue and breast cancer has been investigated.¹⁰ In addition to hormone disruption, they have been connected to cancer, thyroid disorders, skin allergies, and reproductive and neurological issues.¹¹ Paraben residues build up in domestic wastewater and go on to pollute freshwater and disrupt aquatic ecosystems.¹¹

Antibiotic resistance (AMR) is a global health emergency associated with millions of deaths each year. Overuse of antibiotics and antimicrobials in medicine, food production and skin care have led to the emergence of antibiotic-resistant bacteria. Once easily-treatable infections can now be rapidly fatal. According to a review paper in the journal Pathogens¹¹ “cosmetic products may be a source of bacteria with acquired antibiotic resistance, which may be triggered indirectly by the use of human-made preservatives.”

2.1c) Alternatives to preservatives

Are natural alternatives to preservatives effective? They can work well, but a wise man once said “There are no solutions, only trade-offs.” ¹² If we set aside any potential downsides for a moment, common synthetic cosmetic preservatives are extremely effective: highly stable, long lasting, broad spectrum. Natural alternatives may not preserve as comprehensively, nor last as long. Cosmetic producers who wish to utilise natural alternatives may need to consider applying shorter shelf lives to their products. And consumers who prioritise natural cosmetics should take greater care with hygiene and storage in order to get the best out of these products.

Natural alternatives to preservatives include:

• Plant extracts:

  • Polyphenolic compounds are produced by plants as defence mechanisms against things like insects and UV light, and can be effective preservatives. Examples include green tea and lavender extracts, as well as a Manuka honey component (methylglyoxal).¹¹

  • Essential oils have been used in both medicine and cosmetics since the time of the ancient Greeks.¹¹ They contain bioactive compounds (terpenes, ethers, alcohols) with antimicrobial activity.^1,11 Essential oils can sensitise, irritate, or cause phototoxicity to the skin, so the types and amounts must be carefully considered when formulating a product.¹⁰ In early 2026 New Zealand updated its Cosmetic Products Group Standard to follow the IFRA (International Fragrance Association). This identifies any components of essential oils that may cause harm in a dose-dependent manner, and places restrictions on their percentage levels in cosmetic products.

• Peptides: Short protein chains which can be produced in various ways, such as fermenting yeasts.

In addition to preservation, these alternatives can exhibit antioxidant, anti-inflammatory, and soothing properties.¹¹

There are also methods to either eliminate or reduce the need for preservatives:

• ‘Hurdle technology’ refers to the intelligent combination of different preservation factors so that if some microbes survive the first ‘hurdle’ they will be dealt with at subsequent ‘hurdles.’¹⁰

• Good Manufacturing Practice (GMP) includes testing and disinfection.¹⁰ “Cosmetics are produced in a non-sterile but hygienically controlled environment.”⁶

• Packaging:¹⁰ When they encounter a high-fat environment, chemicals from plastic leach into the fats, making glass a better packaging choice for a fat-based product. Glass is more stable and less permeable, therefore offering superior protection against oxidation.

• The form of emulsion matters - if the water and fats are thoroughly emulsified, or the water content is very low there will be less need for preservative compared to a product with a high, or poorly emulsified water content.¹⁰ Low water activity (a_w) means there is minimal water in the product. Microbes require water for growth.¹⁰

• Anhydrous cosmetics such as Kacow! are made without adding any water at all. They are much less susceptible to microbial contamination and growth, and therefore need little or no preservation.¹⁰ The high saturated fat content (and resulting solid form at room temperature) indicates greater stability of the fats. Some plant oils, such as hemp seed oil, are largely unsaturated though, and benefit from the addition of vitamin E to prevent them from oxidising (see the fat notes in the first section).

• Low or high pH: The growth rate of microbes decreases as the pH moves further away from neutral (pH 7). Herein lies another tradeoff, because extremes of pH will irritate and even burn the skin.¹⁰ More acidic products (pH less than 7) tend to be less disruptive to the cutaneous microbiome than more alkaline applications.¹

• Consumer behaviour makes a difference too. Careful storage will extend the shelf life of naturally preserved products. A cool, dark place (sometimes the fridge) is usually ideal. The humidity in bathrooms may not be optimal, but it is a convenient place to store cosmetics, so manufacturers should assume that their product will need to maintain stability in this environment. Hygiene rules such as keeping the lid on between uses, and washing hands before dipping a finger into the jar are recommended.⁶

2.2) Emulsifiers & emollients

Emollient is such a lovely word — a linguist might call it phonaesthetic (when the sound of a word evokes the same kind of sensation as the meaning of the word). Emollients soften and smooth the skin by filling tiny gaps between dry skin cells and reducing water loss. They have been shown to ameliorate atopic dermatitis (the most common form of eczema) via skin acidification and an increase in microbial diversity.¹

There are many synthetic emollients available for use in skincare (including silicone and petroleum based versions). But because most fats and oils will act as an emollient it is easy and safe to opt for natural emollients (as long as fat stability is accounted for). Beef tallow, cacao butter, and plant oils (such as extra virgin olive oil, castor oil, coconut oil and hemp seed oil) are highly effective emollients. All of the ingredients in Kacow! have emollient properties except for the tapioca and essential oils.

An emulsifier is an ingredient that allows oil and water to mix into a stable emulsion, preventing them from separating. There are a lot of synthetic emulsifiers on the market. They do a great job at emulsifying, however there is controversy hanging over many of them. For example, triethanolamine has the potential to form carcinogenic compounds and its usage is restricted in some countries. Some emulsifiers act like a detergent and disrupt the cutaneous microbiome.

Nonionic emulsifiers based on fatty alcohols and fatty acids (such as OliveM 1000) resemble skin lipids and help maintain skin integrity.¹ Kacow! does not need an emulsifier because it is anhydrous, however it contains OliveM 1000 for its emollient and textural qualities. There are many other ingredients which can serve as both emollients and emulsifiers. Fatty acids found in tallow (such as stearic, palmitic and myristic acids) are excellent emollients but also have some level of emulsifying activity.¹

There are plenty of synthetic preservatives, emollients and emulsifiers which have been used in cosmetics and later restricted or banned when more became known about their effects on human health and the environment. Having said that, the same is true for some natural ingredients. Lead was used in cosmetics and topical preparations for thousands of years before we learned how dangerous it was. ‘Natural’ is not uniformly synonymous with ‘safe.’ Evolutionary principles may offer a useful framework for selecting natural skincare ingredients which are safe: If the ingredient is something that humans have evolved to eat (such as a non-toxic plant, or an herbivorous ruminant animal), then it is more likely to be safe to apply it to skin. Evolutionary principles on their own are not adequate though, because skin care tends to be stored rather than made fresh every time you use it, thus preservation and stability still need to be considered carefully for natural ingredients. A sardine is full of fabulous oils, is great for us to eat and it would be perfectly safe to get sardine oil on your face - but if you kept a jar of dead sardines in your bathroom cupboard and smeared a chunk of them on your face each morning, you may stumble across a few issues over time! The perfect recipe is the right mix of natural and rational.