Ep 5: Preservatives - Keeping Bugs Out of Our Cosmetics

It is officially spooky season, and as cosmetic formulators, we can’t think of anything spookier than little microorganisms growing in my cosmetic products. As a consumer, you might not think about this often, but it’s a bigger deal than you might think - bacteria, fungus and other microbes can contaminate your cosmetic products and cause scary consequences like allergies, infections, and even death.   

But you don’t have to worry, because we as formulators have a secret weapon - preservatives! Today we’re going to talk about what preservatives are, why they’re an essential part of your formula, some horror stories of products that didn’t have proper preservative systems, and what you can do as a consumer to make sure you’re using products that are safe and effective.

What Are Preservatives?

Preservatives are additives that prevent decay, discoloration, and spoilage. In cosmetics, they protect water-containing products from bacteria, yeast, and mold - because nobody wants little bugs and fungus growing in their cosmetic products.

Why Do Products Need Them?

Microbes can break down ingredients, create odor or color change, and can make active ingredients effective (and who wants that?) They can also produce toxins or cause eye and skin infections. Different product types have different risks; eye products, lotions/creams, liquid foundations, wipes/sprays, and baby/clinical items are at the highest risk for microbial contamination. Products like anhydrous balms/oils, sticks, hot-pour lipsticks are lower risk, but can still grow microorganisms if water gets introduced at any point.

How Do Microbes Get In?

Sources include contaminated raw materials or water, poor manufacturing or storage, weak preservation, leaky packaging, and grubby fingers in jars. Once microbes reach a water phase of a product, they can grow and multiply quickly if the product's preservative system isn't strong.

Quick Science: Water Activity

Cells pull available water across their cell membranes to grow; after all, they've got to drink too! When outside water activity is low, microbes face something called osmotic stress and go dormant (not dead). The minimum amount of water a microbe needs varies by the microbe; many molds/yeasts grow at lower levels than most bacteria.

Common Preservation Approaches

There are a few different types of preservatives: the biggest players are antibacterial (they target bacteria) and antifungal (they target fungus). There are preservatives that are also broad spectrum, which can wipe out both bacteria and fungus - they're the big dogs. There are also other ingredients that aren't preservatives by themselves, but can support a preservative system; these are ingredients like chelators, which bind to metals that microbes feed on, and glycols, which can reduce water activity and help with overall stability. Products often use a combination of these different types of preservatives, and not all preservative systems are created equal.

How Companies Test Preservation

Preservative Efficacy (Challenge) Tests: Introduce known microbes into a product and count how many are killed off over a certain period of time (usually around a month).

Microbiological Quality (Limits) Tests: routine counts for bacteria/yeast/mold and pathogen screens. Basically just a daily check-in to see if microorganisms are growing in the product.

Accelerated Stability: Putting the product through heat/freezing cycles to predict the product's shelf life (often 3–6 months accelerated). Many brands also test retain samples after launch; unexpected growth can trigger recalls and reformulations if the microbial amounts are high enough.

Parabens: Context, Not Panic

Parabens have been used since the 1920s, often effective near ~0.1%, and are broad spectrum. Beyond rare contact allergy (usually on broken skin), consistent harm in normal use hasn’t been shown. A 2004 paper fueled fear but did not establish causation; the market moved “paraben-free” anyway, often to less-studied, sometimes weaker systems. Be sure to check out part 2 of this series where we do a deep dive into parabens!

When Preservation Fails, Things Get Scary

Unpreserved mascaras have supported growth of eye pathogens; stopping the use of the mascara resolved infections in users. A contaminated mascara plus a corneal scratch led to a severe eye infection and lasting vision changes in one case. Hospital outbreaks have been traced to contaminated body milks/shampoos, showing that non-sterile cosmetics can have really dangerous consequences for immunocompromised patients.

What Consumers Can Do

Be wary of “preservative-free” claims on water-based products and blanket “clean” messaging that rejects proven systems. Don’t dilute products or add water, as this can dilute the preservative system and provide more water for microbes to thrive in. Close the caps of your products immediately; microbes be flying around in the air too. Avoid jars in the shower, and replace eye makeup about every 3 months - NO EXCUSES. Discard any products with off-smell, bulging, color shift, or separation. If you're immunocompromised, choose pumps, single-dose, or sterile-pack formats to stay as safe as possible.

Conclusion

Preservatives keep water-based cosmetics safe. They stop bacteria and fungi from turning products into petri dishes. We covered how microbes get in, why water activity matters, and why packaging and habits can change the risk. We also talked about some cases of when poorly preserved products can have spooky consequences, and what you can do as a consumer to avoid these. 

Safe products use science-based preservative systems, not magic. Good formulas, smart packaging, and your handling habits work together to make sure your products are as safe as they can be. 

Bibliography

1. “Preservatives for Cosmetic Formulations.” SpecialChem, n.d. Accessed Sept 25, 2025.https://www.specialchem.com/cosmetics/guide/preservatives-for-cosmetic-formulations?utm

2. Sole-Smith, Virginia. “Parabens Are Not the Problem.” Allure, 2019. Accessed Sept 25, 2025.https://www.allure.com/story/parabens-are-not-the-problem

3. Allure Editors. “Suntegrity Recalls Impeccable Skin Sunscreen Foundation Over Mold.” Allure, 2024. Accessed Sept 25, 2025.https://www.allure.com/story/suntegrity-sunscreen-mold-recall

4. Allure Editors. “Kosas Revealer Concealer Mold Concerns.” Allure, 2022. Accessed Sept 25, 2025.https://www.allure.com/story/kosas-revealer-concealer-mold

5. “Microbiological Safety and Cosmetics.” U.S. Food & Drug Administration (FDA), n.d. Accessed Sept 25, 2025.https://www.fda.gov/cosmetics/potential-contaminants-cosmetics/microbiological-safety-and-cosmetics?utm

6. “Microbial Growth and Water Activity.” AQUALAB Knowledge Base, n.d. Accessed Sept 25, 2025.https://aqualab.com/en/knowledge-base/expertise-library/microbial-growth

7. “F.D.A. Curbs Use of Germicide Tied to Infant Deaths: Hexachlorophene.” The New York Times, Sept 23, 1972. Accessed Sept 25, 2025.https://www.nytimes.com/1972/09/23/archives/fda-curbs-use-of-germicide-tied-to-infant-deaths-hexachlorophene.html

8. Martin, E. et al. “Outbreak of Burkholderia cepacia in an ICU Linked to Contaminated Body Milk.” Critical Care, 2006. Accessed Sept 25, 2025.https://ccforum.biomedcentral.com/articles/10.1186/cc6778

9. “Can Your Cosmetics Kill You?” Formula Botanica, n.d. (Note: We do not necessarily agree with this site’s stance on “natural/organic” claims.) Accessed Sept 25, 2025.https://formulabotanica.com/can-your-cosmetics-kill-you/

10. ISO 11930:2019 — Cosmetics — Microbiology — Evaluation of the Antimicrobial Protection of a Cosmetic Product. International Organization for Standardization, 2019. Accessed Sept 25, 2025.https://cdn.standards.iteh.ai/samples/75058/56342a9f78034ffdb976290d990dbbb1/ISO-11930-2019.pdf?utm

11. “Stability Testing of Cosmetics.” UL Prospector (presentation), 2015. Accessed Sept 25, 2025.https://www.ulprospector.com/knowledge/media/2015/06/PR-Stability-Presentation2015.pdf