A stability study can provide valuable information for product development.
But when a formulation changes, an important question follows:
Can you simply use the stability data from the old product?
Sometimes, yes.
Often, not without further assessment.
The answer depends on what changed, how significant the change was, and whether the existing data are still representative of the new product.
This matters across cosmetics, food supplements, pharmaceuticals and other regulated products. Stability data are intended to show how product quality changes over time under defined conditions. For medicines, the EMA’s current guidance explicitly takes a risk-based approach to determining what stability data are needed after product changes. European Medicines Agency (EMA)
Stability data belong to a specific product
A stability study does not simply prove that an ingredient is stable.
It provides evidence about a specific product under specific conditions.
That includes factors such as:
- formulation
- manufacturing process
- packaging
- storage conditions
- batch characteristics
- test parameters
- proposed shelf life
Change one of these factors and the relevance of the original study may need to be reconsidered.
So an old stability report is not automatically transferable to a new formulation.
What makes an old study relevant?
Before reusing existing stability data, ask:
Is the new product sufficiently comparable to the product that was tested?
That means looking beyond the product name.
Compare:
- qualitative composition
- quantitative composition
- active ingredients
- excipients
- preservatives
- pH
- manufacturing process
- dosage form
- packaging
- storage conditions
- specifications
The more significant the differences, the weaker the justification for relying solely on the old data.
A small change is not always a small change
Consider a cosmetic cream.
The company replaces one emulsifier with another.
On paper, the formula looks almost identical.
However, the new emulsifier could affect:
- viscosity
- emulsion stability
- appearance
- pH
- preservative performance
- packaging compatibility
The old stability study may still provide useful background information.
It does not automatically prove that the new formulation will remain stable for the same period.
European guidance on cosmetic safety specifically recognises that stability testing should be adapted to the product and its intended use, including the effects of packaging and storage conditions. Binnenmarkt, Industrie, Unternehmertum und KMUs
Formula changes need a stability risk assessment
The right response to a formulation change is not always:
“Repeat the entire study.”
That can be unnecessary.
Instead, first assess the potential impact of the change.
For example:
Low stability impact
A change that is unlikely to affect stability may require only documented justification and targeted verification.
Moderate stability impact
A change that could affect specific quality attributes may require additional testing.
High stability impact
A major formulation or manufacturing change may require a new or substantially expanded stability programme.
This risk-based approach is also reflected in current pharmaceutical stability guidance. The EMA’s 2026 variation guideline provides different expectations depending on whether a change can affect product stability. European Medicines Agency (EMA)
Packaging can change the answer
Even when the formula stays exactly the same, a packaging change can affect stability.
Consider a product moving from:
glass → plastic
or:
jar → airless dispenser
The new packaging can change the product’s exposure to:
- oxygen
- moisture
- light
- evaporation
- mechanical stress
There can also be compatibility considerations between the formulation and the packaging material.
For cosmetics, EU scientific guidance recommends considering stability in the actual container intended for marketing because the packaging itself can influence product stability. Public Health
So an old study using different packaging may not fully represent the new product.
What about changing the supplier?
A supplier change can look minor.
However, the new raw material may have different:
- impurity profiles
- physical properties
- particle size
- moisture content
- manufacturing process
Those differences can affect the finished product.
For pharmaceutical products, the EMA specifically notes that changes to an active substance’s quality characteristics or manufacturer may require additional stability data when the change could affect finished-product stability. European Medicines Agency (EMA)
The same principle is useful more broadly:
A new supplier should trigger a stability impact assessment when the material could influence product behaviour.
What if the active ingredient stays the same?
That does not automatically make the old study transferable.
Imagine a supplement containing the same active ingredient as before.
The company changes:
- capsule shell
- excipients
- flavour
- tablet compression
- moisture protection
The active ingredient has not changed.
Yet the product’s stability profile might.
Stability belongs to the finished formulation, not simply to one ingredient.
What if only the concentration changes?
A concentration change can also matter.
Increasing an active ingredient can affect:
- degradation
- solubility
- pH
- interactions
- moisture sensitivity
- physical stability
Reducing the concentration can create different issues.
Therefore, even a seemingly simple quantitative change should be assessed rather than automatically covered by the old study.
Cosmetics: can the old study support a reformulation?
Sometimes it can support the development process.
For example, existing data may provide useful information about:
- known degradation pathways
- sensitive ingredients
- packaging behaviour
- expected storage conditions
- relevant analytical parameters
However, the final safety and product documentation needs to reflect the actual product placed on the market.
The European Commission states that cosmetic manufacturers are responsible for ensuring that products undergo a scientific safety assessment before being placed on the EU market. Binnenmarkt, Industrie, Unternehmertum und KMUs
Therefore, old data can be supporting evidence, but they should not automatically be treated as proof for a different formulation.
Pharmaceuticals have a more formal framework
For medicines, stability data are closely linked to the registered product and its lifecycle.
The EMA’s current variation guideline, legally effective from January 2026, provides guidance on stability data required when changes are made to authorised medicinal products. European Medicines Agency (EMA)
The underlying principle is straightforward:
The greater the potential impact of the change on stability, the stronger the need for new supporting data.
For example, the EMA guidance identifies situations where changes to the active substance’s quality characteristics could affect finished-product stability and recommends additional stability data. European Medicines Agency (EMA)
The container closure system matters
For pharmaceutical products, stability data are expected to reflect the product and its proposed container closure system.
EMA guidance on existing active substances and finished products states that stability studies should be based on the properties of the active substance and dosage form, while stability data submitted for a product should represent the formulation and container closure system intended for marketing. European Medicines Agency (EMA)
That makes the following comparison important:
Same formulation + different packaging
is not necessarily equivalent to:
Same formulation + same packaging.
Can you use part of an old stability study?
Yes, potentially.
Existing data can remain valuable even when additional testing is required.
For example, an old study might establish:
- known degradation pathways
- suitable analytical methods
- sensitive quality attributes
- expected storage behaviour
- baseline performance
New studies can then focus on the areas affected by the change.
This can be much more efficient than starting from zero.
What if the old product was very similar?
Similarity helps.
However, it needs to be demonstrated rather than assumed.
A useful comparison can include:
| Factor | Old product | New product |
|---|---|---|
| Formula | Compare | Compare |
| Active content | Compare | Compare |
| Excipients | Compare | Compare |
| Manufacturing | Compare | Compare |
| Packaging | Compare | Compare |
| Storage | Compare | Compare |
| Specifications | Compare | Compare |
| Key stability risks | Assess | Assess |
The result can then support a documented stability risk assessment.
Stability testing is not only about appearance
A product can look unchanged and still have stability problems.
Depending on the product, relevant parameters may include:
- active content
- degradation products
- pH
- viscosity
- moisture
- microbiological quality
- appearance
- odour
- dissolution
- physical properties
The relevant tests should reflect the product’s known risks.
For cosmetics, EU scientific guidance lists physical and chemical characteristics such as appearance, pH and viscosity among parameters that may need to be monitored. Public Health
A product can fail stability without looking different
Imagine a supplement that still looks identical after six months.
Its active ingredient concentration has nevertheless fallen below specification.
Visually, nothing changed.
Analytically, the product is no longer within its defined quality requirements.
That is why stability studies need relevant analytical measurements, not just visual inspection.
Microbiological stability matters too
For products that can support microbial growth, microbiological stability is another consideration.
A formulation change can alter:
- preservative effectiveness
- water activity
- pH
- moisture
- microbial susceptibility
Consequently, a previous stability study may not fully cover a reformulated product.
The appropriate microbiological testing depends on the product category and formulation.
What about shelf life?
This is where the distinction becomes particularly important.
A previous product may have demonstrated:
24-month shelf life.
That does not automatically mean the reformulated product has the same shelf life.
The new formulation needs sufficient evidence to justify the proposed storage period.
For medicinal products, stability data are specifically used to establish or support shelf life and storage conditions. European Medicines Agency (EMA)
The same basic scientific principle applies across product development:
Shelf life needs evidence.
Accelerated stability data can help
Accelerated studies expose products to elevated conditions to investigate how they behave under stress.
They can provide useful information during development.
However, accelerated data should not automatically be treated as a direct substitute for long-term evidence.
The study design and interpretation need to match the purpose of the assessment.
For medicines, the EMA’s stability guidance explicitly considers long-term, accelerated and intermediate conditions as part of stability programmes. European Medicines Agency (EMA)
When do you need a new stability study?
A new or expanded study becomes more likely when the change affects factors such as:
- formulation
- active concentration
- preservative system
- manufacturing process
- critical raw materials
- packaging
- storage conditions
- dosage form
- product specifications
The exact requirement depends on the product category and the significance of the change.
That is why a stability impact assessment should come first.
When might additional testing be limited?
Additional testing may be more limited when:
- the formulation is unchanged
- the manufacturing process is unchanged
- the packaging is unchanged
- only a low-risk administrative detail changes
- the change has been scientifically demonstrated not to affect stability
Current ICH stability guidance for medicines explicitly describes a risk-based approach in which changes with no expected impact on stability may not require additional stability data, provided the assessment supports that conclusion. European Medicines Agency (EMA)
The important words are:
“provided the assessment supports it.”
It should be justified, not assumed.
A practical decision tree
When you have an old stability study, ask:
1. Is the formula identical?
If yes, continue.
If no, assess the formulation change.
2. Is the packaging identical?
If no, assess compatibility and stability impact.
3. Is the manufacturing process identical?
If no, assess whether the change can affect product quality.
4. Are the specifications identical?
If no, determine which quality attributes have changed.
5. Has the intended shelf life changed?
If yes, additional evidence may be required.
6. Can the existing data scientifically represent the new product?
If not, generate additional stability data.
This approach is much more defensible than simply reusing an old report.
What should you document?
A stability bridging decision should be traceable.
Document:
- what changed
- why it changed
- what remained unchanged
- potential stability risks
- existing supporting data
- additional tests considered
- final decision
- scientific justification
This makes the decision easier to defend during an audit or regulatory review.
The biggest mistake: treating “similar” as “identical”
Two products can be extremely similar.
That does not automatically make their stability behaviour identical.
For example:
95% identical formula
does not necessarily mean:
95% of the stability evidence can simply be transferred.
One changed ingredient could be critical.
One packaging change could alter oxygen exposure.
One process change could affect degradation.
The importance of the change matters more than the percentage of the formula that stayed the same.
The smarter approach: bridge where possible
The answer is not always to throw away existing data.
Instead, use it intelligently.
Existing stability data can provide a baseline.
Then targeted testing can address the specific uncertainties introduced by the new product.
For example:
Old product data
formulation comparison
risk assessment
targeted additional testing
=
stronger evidence for the new product
This can save both time and resources while maintaining a defensible scientific basis.
Why this matters for product development
Stability testing takes time.
If you wait until the product is almost ready for launch, discovering a stability problem can force changes to:
- formulation
- packaging
- shelf life
- storage conditions
- specifications
- regulatory documentation
Starting the stability assessment early gives R&D more options.
It also makes the launch timeline more predictable.
The Makrolife approach
Makrolife supports stability and compatibility studies for products including cosmetics and pharmaceutical products, alongside analytical and regulatory services.
The useful question is not simply:
“Do we need a new stability study?”
It is:
“What evidence do we already have, what has changed, and what additional data are needed to support the new product?”
That distinction allows stability testing to become part of product development rather than a late-stage obstacle.
The bottom line
Can you use an old stability study for a new product?
Sometimes.
But you should not assume that previous data automatically transfer.
First, compare the old and new products. Then assess changes to the formulation, manufacturing process, packaging, specifications and storage conditions. If the changes could affect stability, additional data may be needed.
Existing studies can still be valuable.
They can provide baseline information and help define targeted follow-up testing.
The goal is therefore not:
“Repeat everything.”
It is:
“Generate enough relevant evidence to demonstrate that the new product remains stable for its intended shelf life.”
That is the difference between reusing old data and scientifically bridging stability evidence.