Can the concentration of active ingredients change later?

Yes, the concentration of active ingredients in a cosmetic formula can change after initial development, but it is never a simple adjustment. Modifying an active ingredient percentage affects the formula’s stability, safety profile, and regulatory standing, which means any change must be treated as a reformulation rather than a quick tweak. The questions below unpack exactly what drives those changes and what to expect from the process.

What factors determine active ingredient concentration in a formula?

Active ingredient concentration in a cosmetic formula is determined by a combination of efficacy targets, regulatory limits, ingredient compatibility, and overall formula stability. The starting point is always the intended function of the ingredient: a moisturising agent, a preservative, and a botanical extract each have different effective dose ranges that guide where the percentage should sit.

Beyond efficacy, several practical factors shape the final concentration:

Regulatory maximum limits: Many active ingredients, particularly those with functional or borderline drug-like effects, are subject to concentration caps set by regional regulations such as the EU Cosmetics Regulation.
Ingredient interactions: Some actives react with other components in the formula. A higher concentration of one ingredient may destabilise another, alter the pH balance, or cause phase separation.
Skin tolerance and safety data: Safety assessments define the maximum safe-use level for each ingredient. Exceeding those levels requires additional safety justification.
Cost and sourcing: High-quality, ethically sourced natural actives can be expensive. Concentration decisions often reflect a balance between clinical effectiveness and commercial viability.
Sensory and aesthetic outcomes: In natural cosmetics especially, a higher concentration of a botanical extract might change the product’s colour, scent, or texture in ways that affect consumer experience.

All of these factors interact with each other, which is why determining the right concentration is a formulation decision that requires both scientific knowledge and practical experience.

Can you increase or decrease an active ingredient percentage after production?

You can adjust active ingredient concentration after a formula has been produced, but doing so means creating a new formula version rather than modifying existing batches. Once a product has been manufactured, the concentration in those units is fixed. Any change in percentage applies only to future production runs and triggers a full reformulation process.

Whether you want to increase or decrease a concentration, the implications differ:

Increasing the concentration

Raising the percentage of an active ingredient may strengthen the product’s efficacy claim, but it also increases the risk of irritation, incompatibility with other ingredients, or regulatory non-compliance if the new level approaches or exceeds a permitted maximum. The entire formula needs to be re-evaluated with the higher concentration in place.

Decreasing the concentration

Lowering a percentage may seem less risky, but it can undermine the product’s performance and, depending on how the product is marketed, may affect the validity of existing efficacy claims. If the active ingredient also serves a preservative function, reducing it could compromise microbiological safety.

In both cases, the change cannot be made in isolation. The full formula must be reviewed, retested, and revalidated before the updated version enters production.

What happens to a formula’s stability when concentrations change?

Changing the concentration of an active ingredient almost always affects a formula’s stability, and the impact can be unpredictable without proper testing. Stability in cosmetic formulation refers to how well a product maintains its intended physical, chemical, and microbiological properties over time. Altering one ingredient’s percentage shifts the balance of the entire system.

Common stability effects include changes in viscosity, emulsion separation, colour shifts, pH drift, and altered preservation efficacy. In natural cosmetics, where synthetic stabilisers are avoided, these effects can be more pronounced because the formulation relies on a precise interaction between natural emulsifiers, thickeners, and actives.

This is why any change in active ingredient concentration must be followed by new stability testing, typically including:

Accelerated stability testing at elevated temperatures
Real-time stability testing over the intended shelf life
Freeze-thaw cycling to assess physical resilience
Microbiological challenge testing if preservation is affected

Skipping this step is not an option. A formula that looks identical on paper may behave very differently in real conditions once a concentration has shifted.

Does changing concentration require new regulatory approval?

In the EU, changing the concentration of an active ingredient in a cosmetic product requires updating the product’s safety documentation and, in most cases, its Cosmetic Product Safety Report (CPSR). This report must be reviewed and signed off by a qualified safety assessor before the updated product can legally enter the market. It is not a full approval process in the pharmaceutical sense, but it is a mandatory step that cannot be bypassed.

The extent of the regulatory work depends on the nature of the change. A minor reduction in a well-studied botanical extract may require only a targeted update to the safety report. A significant increase in a functional active, or any change that pushes a concentration closer to a regulatory limit, will require more comprehensive documentation and potentially new safety data.

Notification through the EU’s Cosmetic Products Notification Portal (CPNP) must also be updated to reflect the reformulated product. Selling a product with a concentration that no longer matches its notified formula is a compliance violation, regardless of whether the change seems minor.

How long does it take to reformulate with a different concentration?

Reformulating a cosmetic product with a different active ingredient concentration typically takes between two and six months, depending on the complexity of the formula and the extent of testing required. This timeline accounts for the formulation work itself, stability testing, safety assessment, and regulatory documentation.

The main phases and their approximate durations are:

Formulation adjustment and initial testing (two to four weeks): The formula is reworked at the new concentration, and preliminary bench tests are conducted to assess compatibility and sensory properties.
Stability testing (one to three months): Accelerated and real-time stability studies run in parallel. This phase is often the longest because it cannot be significantly compressed without compromising data quality.
Safety assessment update (two to four weeks): A qualified safety assessor reviews the updated formula and revised stability data to produce or update the CPSR.
Regulatory notification update (one to two weeks): The product’s CPNP notification is updated before the reformulated product is placed on the market.

Timelines can be shorter for straightforward changes with well-documented ingredients, and longer when new raw materials are introduced or when the change triggers additional safety questions. Planning ahead and working closely with your formulation partner from the start is the most effective way to keep the process on track.

How Rebel Nature helps with active ingredient reformulation

At Rebel Nature, we work with brands at every stage of the reformulation process, from the initial decision to adjust a concentration through to stability testing, safety documentation, and production. Our team of experienced formulators understands the particular challenges of natural cosmetics, where ingredient interactions can be more complex and the margin for error is smaller.

Here is what we offer when you need to change an active ingredient percentage:

Expert formulation review: We assess the impact of the proposed concentration change on the full formula before any lab work begins, so you understand the implications upfront.
Stability testing: We run the full range of stability studies in-house, giving you reliable data without outsourcing delays.
Safety and regulatory guidance: We help you navigate the documentation requirements, including CPSR updates and CPNP notifications, so your reformulated product is market-ready.
Flexible production runs: Whether you need a small pilot batch to validate the new formula or a full production run, our capabilities scale to your needs.
Ingredient sourcing support: With a portfolio of over 500 natural raw materials, we can recommend high-quality alternatives if a concentration change requires a different or complementary ingredient.

If you are considering adjusting the active ingredient concentration in one of your formulas, the best first step is a conversation with our team. Get in touch with Rebel Nature to discuss your reformulation needs and find out how we can help you move forward efficiently and compliantly.

Frequently Asked Questions

Can I change the active ingredient concentration without telling my contract manufacturer?

No — your contract manufacturer needs to be informed of any concentration change before production begins, as it directly affects how the formula is manufactured and quality-controlled. Proceeding without notifying them risks producing a batch that does not match your updated safety documentation or CPNP notification, which is a compliance violation. A good manufacturing partner will also flag potential production-side issues with the new concentration, such as mixing challenges or raw material handling requirements, that you may not anticipate from the formulation side alone.

What is the difference between a reformulation and a minor formula adjustment?

In practice, there is no such thing as a truly minor formula adjustment when it comes to active ingredient concentration — any change in percentage constitutes a reformulation that requires retesting and updated documentation. The distinction matters because brands sometimes assume small percentage shifts (for example, moving from 2% to 2.5%) can be made informally, but regulators and safety assessors treat any change to a notified formula as a material update. The scale of the work required may vary, but the process itself — review, testing, updated CPSR, updated CPNP notification — remains the same regardless of how small the change appears.

How do I know if my current active ingredient concentration is actually working?

The most reliable way to evaluate whether your current concentration is delivering the intended effect is through consumer perception studies or, where applicable, in-vitro or in-vivo efficacy testing conducted at the formulated concentration. Ingredient supplier data is a useful starting point, but it reflects the ingredient in isolation — not how it performs within your specific formula matrix. If you have doubts about efficacy at your current level, a formulation review can help determine whether a concentration adjustment is warranted or whether other formula factors are limiting performance.

What are the most common mistakes brands make when trying to adjust active ingredient concentrations?

The most frequent mistake is treating a concentration change as an isolated tweak rather than a full reformulation, which leads to skipped stability testing, outdated safety documentation, and potentially non-compliant products on the market. Another common error is making the change reactively — for example, in response to a cost pressure or supplier issue — without first assessing the downstream impact on efficacy claims, formula stability, and regulatory standing. Working with an experienced formulation partner from the outset of any concentration discussion helps avoid these pitfalls before they become costly problems.

If my active ingredient supplier changes the raw material's specification, do I need to go through the same reformulation process?

Yes, a significant change in raw material specification — such as a shift in active content percentage, extraction method, or country of origin — can effectively alter the functional concentration of that ingredient in your formula, even if your stated percentage on paper remains the same. This type of change should trigger a review of your safety documentation and, depending on the extent of the specification shift, may require updated stability testing and a revised CPSR. Always request a change notification from your supplier and share it with your formulation partner and safety assessor promptly so they can advise on the required next steps.

Can I run a small test batch at a new concentration before committing to a full reformulation process?

Yes, running a pilot or laboratory-scale batch at the adjusted concentration is actually a recommended first step before committing to the full reformulation timeline and cost. A small-scale batch allows your formulation team to assess immediate compatibility, sensory properties, and any obvious stability red flags before investing in formal stability studies. However, it is important to understand that a pilot batch does not replace the full testing and documentation process — it simply provides early directional data to confirm the adjustment is worth pursuing.

Does changing an active ingredient concentration affect the product's marketing claims?

It can, particularly if the existing claims are tied to the specific concentration of the active ingredient — for example, a claim referencing a clinically studied percentage of a key ingredient. If you reduce the concentration below the level at which efficacy data was generated, those claims may no longer be substantiated and would need to be revised or removed to remain compliant with EU cosmetic claims regulations. Conversely, increasing a concentration may allow for stronger claims, but any new claim must be supported by appropriate evidence at the updated level before it can be used in marketing.