In most cases, replacing an ingredient in a cosmetic formulation does require some form of additional assessment, and often additional testing. Whether a full retesting program is necessary depends on how significant the change is, how different the new ingredient is from the original, and what role that ingredient plays in the product’s safety and stability profile. Even a seemingly minor swap can have implications under EU cosmetics law. The sections below unpack the key questions formulators, brands, and safety assessors face when considering a cosmetic ingredient substitution.
A significant ingredient change in cosmetics is any substitution that alters the product’s safety, stability, performance, or regulatory status. This includes swapping an active ingredient, changing a preservative, replacing a functional component with a different chemical structure, or introducing an ingredient with a different concentration or origin. Even a change in supplier for the same ingredient can qualify if the purity profile or specification differs.
Not every change is automatically significant. Replacing one ingredient with another that shares an identical chemical identity, the same concentration, and a comparable safety and quality profile may be treated as a minor variation. However, the threshold for what counts as significant is interpreted conservatively under EU regulations, which means formulators should always document the rationale for classifying a change as minor rather than assuming it is.
Factors that typically push a change into the significant category include:
Replacing an ingredient does not always require a full new round of safety testing, but it always requires a safety assessment review. Under EU cosmetics law, every cosmetic product must have an up-to-date Product Information File (PIF) and a valid safety assessment. When an ingredient changes, the responsible person must evaluate whether the existing safety data still hold, which in practice means the cosmetic safety assessor must review and often update their report.
Whether new laboratory tests are commissioned depends on the outcome of that review. If the replacement ingredient has a well-established safety profile, is used at a comparable concentration, and does not interact differently with the other components in the formulation, the assessor may be able to rely on existing data. If gaps exist, new tests will be required before the product can legally remain on or be placed on the EU market.
After a cosmetic formulation change, the tests that may be needed fall into three broad categories: stability testing, microbiological or challenge testing, and safety or toxicological assessment. Which of these are required depends on the nature of the ingredient substitution and the product type.
Stability testing checks that the reformulated product maintains its physical and chemical integrity over time. Even a like-for-like ingredient swap can shift a product’s pH, alter its emulsion structure, or affect its colour and scent. A new accelerated stability study is usually recommended after any formulation change to confirm the product remains within specification throughout its intended shelf life.
If the substituted ingredient plays any role in preservation, or if the new ingredient interacts with the existing preservative system, a new challenge test is typically required. This applies particularly to natural cosmetics reformulation, where preservation systems are often more complex and sensitive to changes in the ingredient matrix.
The safety assessor will review the toxicological profile of the new ingredient, including any available data on skin sensitisation, irritation, and systemic exposure. If the ingredient is novel or lacks sufficient existing safety data, additional in vitro or in silico studies may be commissioned to fill those gaps.
EU cosmetics law, governed by Regulation (EC) No 1223/2009, does not set out a specific procedure for ingredient substitutions, but it establishes the framework that makes retesting or reassessment necessary. The regulation requires that every cosmetic product placed on the EU market is safe for human health, supported by a Product Information File, and assessed by a qualified cosmetic safety assessor. When an ingredient changes, these obligations do not pause.
In practical terms, the responsible person (the EU-based entity legally accountable for the product) must ensure the PIF reflects the current formulation at all times. If an ingredient substitution is made and the PIF is not updated, or if the safety assessment no longer accurately reflects the product, the responsible person is in breach of the regulation. Enforcement authorities can request access to the PIF at any time, so documentation of every formulation change and the rationale behind it is not optional.
The regulation also contains specific provisions for restricted and prohibited substances. If the replacement ingredient appears on the restricted substances list (Annex III) or is subject to concentration limits, compliance with those limits must be verified for the new formulation before the product is sold.
A true like-for-like swap, where the replacement ingredient is chemically identical, used at the same concentration, sourced to the same specification, and has an equivalent or better safety profile, can in some cases avoid new laboratory testing. However, it cannot avoid a safety assessment review. The assessor must formally confirm that the existing data remain valid for the substituted ingredient before the product continues to be sold.
In practice, genuine like-for-like swaps are less common than they appear. Natural ingredients in particular can vary between suppliers in ways that matter: differences in batch composition, extraction method, or country of origin can affect both the ingredient’s efficacy and its safety profile. What looks like a straightforward substitution on paper may still require the assessor to gather new supplier documentation, updated safety data sheets, and specification certificates before they can sign off.
The safest approach is to involve the safety assessor before the swap is made, not after. Early involvement allows the assessor to identify any data gaps upfront and advise on whether testing is needed, saving time and avoiding the risk of placing a non-compliant product on the market.
The decision on whether retesting is needed after a cosmetic ingredient substitution must be made by a qualified cosmetic safety assessor. Under EU Regulation 1223/2009, the safety assessor must hold a relevant qualification in pharmacy, toxicology, medicine, or a related discipline, and they are the only person legally authorised to sign off on a cosmetic safety assessment report. This is not a decision that can be made unilaterally by a formulator or brand owner.
In practice, the process works best as a collaboration. The formulator provides the technical rationale for the change, the supplier provides updated raw material documentation, and the safety assessor evaluates the combined picture to determine what, if any, additional data or testing is required. Brands working with a contract manufacturer benefit from having access to formulation expertise at this stage, as the manufacturer can often anticipate which changes are likely to trigger retesting requirements and advise accordingly.
When a formulation needs to change, whether due to supply chain disruption, a sustainability goal, or a regulatory update, navigating the process correctly matters. We work with brands throughout the reformulation process to make ingredient substitutions as smooth and compliant as possible. Our team of experienced formulators evaluates each substitution in the context of the full formulation, not just the ingredient in isolation.
Here is what working with us on an ingredient substitution looks like in practice:
Our approach to natural cosmetics formulation is built on transparency and long-term partnership. We do not just hand over a formula and step back. We stay involved, answer questions, and help brands make decisions that are good for their products and compliant with EU law. If you are facing a formulation change and want expert guidance on what it means for your safety testing obligations, get in touch with Rebel Nature and we will help you find the right path forward.
The timeline depends on the complexity of the substitution and whether new laboratory testing is required. A straightforward safety assessment review where existing data are sufficient can take a few weeks, while a full retesting program that includes stability and challenge testing can take three to six months. Involving your safety assessor and contract manufacturer early in the process is the most effective way to avoid unexpected delays, particularly if you are working to a product launch or relaunch deadline.
At a minimum, you should request a full specification sheet, a Safety Data Sheet (SDS), a Certificate of Analysis (CoA), and any available toxicological or safety dossier for the ingredient. If the ingredient is of natural origin, documentation of the extraction method, country of origin, and any relevant allergen declarations is also important. Your safety assessor will need all of this information to evaluate whether the ingredient can be incorporated into the existing safety assessment framework without additional testing.
Continuing to sell a product on the EU market while its Product Information File does not accurately reflect the current formulation is a breach of Regulation (EC) No 1223/2009. If enforcement authorities request access to the PIF and it is out of date or the safety assessment no longer covers the actual formulation, the responsible person can face market withdrawal orders, fines, or other regulatory consequences. The safest approach is to complete the assessment update and confirm compliance before the reformulated product is placed on or continues to be sold on the market.
They can, and this is an aspect that brands often overlook. If the substituted ingredient was the basis for a specific performance or sustainability claim, such as ‘formulated with organic X’ or ‘contains active Y,’ that claim may no longer be accurate or substantiated after the swap. Any claims made about a cosmetic product must be truthful, substantiated, and compliant with EU Regulation No 655/2013 on cosmetic product claims. It is worth reviewing your marketing copy alongside the formulation change to ensure everything remains aligned.
Yes, the product type significantly influences how a substitution is assessed. Leave-on products, such as moisturisers, serums, and sunscreens, carry a higher systemic exposure potential than rinse-off products like shampoos or cleansers, which means the safety assessor will apply a more conservative approach when evaluating the toxicological profile of a new ingredient. The same ingredient substituted into a leave-on formulation may require more supporting data than it would in a rinse-off context, particularly for ingredients with known sensitisation potential or those used near sensitive areas such as the eyes or lips.
The most frequent mistake is treating a substitution as an internal operational decision rather than a regulatory event, and only involving the safety assessor after the change has already been implemented. Other common errors include assuming that a same-INCI ingredient from a different supplier is automatically equivalent without checking specifications, and failing to update the Product Information File to reflect the change. A proactive approach, where the safety assessor and formulator are consulted before any substitution is finalised, avoids the majority of compliance issues and retesting surprises.
The EU Cosmetics Regulation (EC) No 1223/2009 includes a series of annexes that list prohibited substances (Annex II), restricted substances with concentration limits or conditions of use (Annex III), and permitted colorants, preservatives, and UV filters (Annexes IV–VI). Before finalising any ingredient substitution, the replacement ingredient should be checked against these annexes to confirm it is permitted and that it will be used within the specified conditions. Your safety assessor or contract manufacturer can carry out this compliance check as part of the substitution review process.
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