Microbial and Preservative Testing
The two tests that keep a product from growing bacteria and mold, when to run each, the standards to ask your lab for, and which products actually need it.
Anything with water in it can grow bacteria, yeast, and mold, which is why a cosmetic needs testing before it reaches a customer’s face. Two different tests do the job: a challenge test that proves your preservative system actually works, and microbial limits testing that confirms each batch is clean before it ships. Together they are the backbone of proving a product is safe.
What to actually run
Run a challenge test during development. Also called preservative efficacy testing, this deliberately contaminates your formula with microorganisms and measures how well your preservative system kills them off over time. You run it while developing the product, to prove the preservation holds up before you scale. Ask the lab for ISO 11930 or USP <51>, the two standard methods. This same test is what sets your period after opening.
Run microbial limits testing on production batches. Before a batch ships, this confirms the finished product is within acceptable microbial counts and free of the organisms that matter for skin products, like Pseudomonas aeruginosa and Staphylococcus aureus. The standard methods are USP <61> and <62> or ISO 17516. Challenge testing proves the recipe is safe; batch testing proves the batch you actually made is safe.
Send it to a cosmetic microbiology lab. Labs such as Intertek and Eurofins run both tests, and many contract manufacturers include testing as part of production. Build the cost and the timeline into your launch plan, because results take time.
Focus it where the risk is. Water-based products, lotions, serums, cleansers, mists, need robust preservation and full testing. Truly anhydrous products like face oils, balms, and dry powders carry far lower microbial risk, though they can still be tested for peace of mind and retailer requirements.
Why it matters beyond safety
Beyond protecting customers, this testing is part of the safety substantiation that MoCRA now legally requires, and major retailers like Sephora and Ulta ask for microbial and stability data before they will stock a brand. Skipping it is how a product ends up recalled, which costs far more than the testing would have.
Frequently Asked Questions
What is the difference between a challenge test and microbial limits testing?
A challenge test (preservative efficacy testing) proves your preservative system can kill microorganisms over the life of the product, and you run it during development. Microbial limits testing checks that a specific finished batch is within acceptable microbial counts and free of key pathogens, and you run it on production batches before they ship. One validates the formula, the other validates the batch.
What standards should I ask my lab for?
For the challenge test, ISO 11930 or USP <51>. For microbial limits testing, USP <61> and <62> or ISO 17516. A good cosmetic microbiology lab will know these by name, and you should specify which ones you need for your market.
Do all cosmetics need microbial testing?
The products that most need it are water-based, since water lets microbes grow. Lotions, serums, cleansers, and mists need strong preservation and full testing. Truly anhydrous products like oils, balms, and powders are much lower risk, though testing them still supports your safety records and satisfies retailers.
Sources
- ISO 11930:2019, “Evaluation of the antimicrobial protection of a cosmetic product”. The challenge-test standard for preservative efficacy.
- Intertek, “Cosmetics Preservative Efficacy Challenge Testing”. What challenge testing involves and the standards labs test to.