How Is Stability Testing Conducted for Rose Products?
A Scientific Guide to Physical, Chemical and Microbiological Stability, Shelf Life and Packaging Compatibility
A rose water, rose distillate, cream containing rose essential oil, or rose-based serum may have all the desired characteristics on the day it is manufactured. But how will that same product behave weeks, months, or even years later?
Will its colour change? Will its fragrance remain consistent? Will its pH stay within the expected range? Could a cream develop phase separation? Will the product continue to meet microbiological quality requirements? Could its packaging influence its composition?
Stability testing is the scientific and controlled evaluation of how a product changes over time.
One of the principal international references for cosmetic stability evaluation, ISO/TR 18811:2018 — Cosmetics: Guidelines on the Stability Testing of Cosmetic Products, emphasizes that there is no single standardized stability-testing protocol suitable for every cosmetic product.
Cosmetics differ considerably in their formulations, packaging systems, and intended conditions of use. Manufacturers must therefore select and scientifically justify testing methods, specifications, and conditions appropriate to each product.
This principle is particularly important for rose-derived products.
Rose water, rose distillate, rose essential oil, creams, and serums are not chemically or physically identical products. Consequently, their stability does not necessarily need to be evaluated using the same methods or acceptance criteria.
What Is Stability?
In cosmetic science, stability cannot be reduced to the simple question:
“Has the product spoiled or not?”
A stability study examines how well a product maintains its defined characteristics over time under specified storage conditions.
The Cosmetics Europe/CTFA stability guidelines identify four important areas of evaluation:
Physical integrity and stability
Chemical stability
Microbiological stability
Compatibility between the product and its packaging
A comprehensive stability assessment therefore involves more than observing the product's appearance.
Rose Academy Insight
The fact that a product has maintained its original colour and fragrance is a positive observation. However, this alone does not prove that the product has remained chemically or microbiologically stable.
Why Is Stability Important for Rose Products?
Rose-derived products can have very different physical and chemical structures.
For example:
Rose essential oil consists largely of volatile, lipophilic compounds.
Rose water or rose distillate is an aqueous system containing volatile and water-soluble constituents transferred into the water phase during distillation.
Rose-based creams may be emulsions containing both aqueous and oil phases.
Rose serums can exhibit widely differing physicochemical properties depending on their formulations.
Therefore, the expression “rose product” should not be treated as though it describes one uniform product category.
Even two products marketed under the same name, such as rose water, may differ in:
Botanical raw materials
Manufacturing methods
Distillation conditions
Chemical composition
Packaging systems
GC–MS studies of Rosa damascena rose waters have demonstrated differences in chemical composition among commercial samples.
In one study, phenethyl alcohol, geraniol, and β-citronellol were identified among the major constituents of several samples.
The researchers emphasized the importance of chemical analysis for a more detailed assessment of product quality.
This leads to a fundamental scientific principle:
Stability results obtained from one rose water product cannot automatically be generalized to all rose waters.
How Is a Stability Test Planned?
The first step in a scientific stability study is not simply placing a product in a storage cabinet and waiting several months.
A stability-testing protocol must first be established.
According to the approach described in ISO/TR 18811:2018, the manufacturer should define and justify the analytical methods, product specifications, and testing conditions according to the characteristics of the product.
Importantly, the ISO guidance does not establish one universal temperature, testing duration, or acceptance criterion for every cosmetic product.
This is an essential distinction.
For example, a statement sometimes encountered online is:
“Every cosmetic product must be tested at 40°C for three months.”
This is not a universal ISO requirement.
An appropriate stability-testing protocol must be designed according to the product's specific properties and intended use.
1. Establishing the Product's Initial Characteristics
For a stability study to provide meaningful results, the product's initial condition must be documented.
Depending on the product, the following characteristics may be recorded.
Appearance
The presence or absence of:
Clarity
Cloudiness
Sediment
Foreign particles
Colour
The product's initial colour and any subsequent changes during storage.
Fragrance
Whether the characteristic fragrance remains consistent over time.
pH
An important physicochemical parameter, particularly for water-based products.
Viscosity
A useful measurement for evaluating changes in consistency in creams, gels, and similar products.
Phase Structure
In emulsions, the stability of the oil and water phases can be examined to determine whether separation occurs.
Other analytical parameters may also be included depending on the product's particular characteristics.
The objective is to create a documented baseline against which future measurements can be compared.
2. Storing the Product Under Different Conditions
Cosmetic products do not remain in one constant environment throughout their life cycle.
After manufacturing, they may be stored in warehouses, transported, displayed in retail stores, and eventually used in consumers' homes.
During these stages, products may be exposed to environmental factors such as:
Temperature
Light
Air
Humidity
The U.S. Food and Drug Administration (FDA) also notes that temperature changes, sunlight, air, and humidity can contribute to changes in cosmetic products, including their colour, texture, and fragrance.
Certain conditions may also influence microbial growth.
For these reasons, stability studies may examine products under different environmental conditions, depending on the study design.
Room Temperature
Room-temperature testing helps assess how a product behaves under normal storage conditions.
Low Temperature
Cold storage conditions may be used to investigate:
Precipitation
Crystallization
Cloudiness
Changes in emulsion structure
Elevated Temperature
Higher temperatures may accelerate certain physical and chemical changes.
They can therefore be useful in accelerated stability assessments.
Light Exposure
Products containing light-sensitive constituents may be evaluated for possible photochemical changes.
Temperature Cycling
Some stability protocols involve repeatedly exposing products to warm and cold conditions.
This approach can be particularly useful for evaluating the resistance of emulsions and packaging systems.
The Cosmetics Europe guidelines recommend considering stress factors representative of expected storage and use conditions.
They also emphasize monitoring critical product characteristics such as colour, fragrance, texture, and flow properties.
3. Repeating Measurements at Defined Intervals
Stability testing is fundamentally a study of change over time.
For this reason, examining a product only at the beginning and end of a test may not always provide sufficient information.
The study protocol should define appropriate measurement intervals.
At each interval, selected product characteristics are evaluated again and compared with the initial results.
Example of a Simplified Stability Monitoring Schedule
| Evaluation Parameter | Initial Assessment | Intermediate Checks | Final Assessment |
|---|---|---|---|
| Appearance | ✓ | ✓ | ✓ |
| Colour | ✓ | ✓ | ✓ |
| Fragrance | ✓ | ✓ | ✓ |
| pH | ✓ | ✓ | ✓ |
| Physical structure | ✓ | ✓ | ✓ |
| Microbiological quality | ✓ | As appropriate | ✓ |
This table is provided only to illustrate the general approach.
The actual testing frequency, measurement intervals, and parameters must be selected according to the product and its stability-testing protocol.
4. Evaluating Physical Stability
Physical changes are often the first alterations noticed by consumers.
For liquid products such as rose water and rose distillates, stability testing may monitor:
Cloudiness
Precipitation
Formation of particles
Changes in colour
For creams and emulsions, the evaluation may also include:
Phase separation
Changes in viscosity
Oil accumulation on the surface
Loss of homogeneity
The Cosmetics Europe guidelines recommend evaluating sensory and physical characteristics such as colour, fragrance, texture, and flow behaviour, particularly after exposure to stress conditions.
These observations can provide valuable information about the product's physical integrity.
However, physical stability represents only one part of the overall stability assessment.
5. Monitoring Changes in pH
pH is an important monitoring parameter, especially for water-based rose products.
The initial pH value is relevant, but it is not the only consideration.
The more important question is:
Does the product's pH change over time?
For example, the pH measured at the beginning of a stability study can be compared with measurements taken during intermediate assessments and at the end of the testing period.
A significant change may indicate that further investigation is required to identify possible physicochemical or other changes within the product.
However, one common misunderstanding should be avoided:
An acceptable pH value does not, by itself, demonstrate that a product is stable or microbiologically safe.
pH is one component of a broader stability evaluation.
Its significance becomes clearer when interpreted alongside other physical, chemical, and microbiological findings.
6. Monitoring Fragrance and Colour
This aspect of stability testing is particularly important for rose-derived products.
The characteristic sensory properties of rose products are closely associated with their volatile constituents.
Significant changes in fragrance or colour over time should therefore be documented.
However, sensory evaluation and chemical analysis should not be confused.
Research examining Rosa damascena rose waters has indicated that differences in colour and fragrance may provide useful indications of product characteristics.
Nevertheless, a detailed assessment requires appropriate chemical analysis.
Therefore, the statement:
“The fragrance has not changed, so the product must be completely unchanged.”
is not a scientifically sufficient conclusion.
A product may maintain a familiar fragrance while undergoing changes that cannot be detected through sensory observation alone.
7. Evaluating Microbiological Stability
Microbiological quality is particularly important for cosmetic products containing water.
A product may look entirely normal from the outside.
However, appearance, colour, and fragrance alone cannot demonstrate microbiological safety.
Microbiological characteristics are among the important areas considered in cosmetic stability assessment under ISO/TR 18811.
Additional international standards relevant to cosmetic microbiology include:
ISO 17516 — Cosmetics: Microbiology — Microbiological Limits
This standard addresses microbiological acceptance criteria for cosmetic products.
ISO 21148 — Cosmetics: Microbiology — General Instructions for Microbiological Examination
This standard provides general instructions for conducting microbiological examinations of cosmetics.
It is important to distinguish three different concepts:
Stability testing
Microbiological testing
Preservation efficacy testing, also known as challenge testing
These are not interchangeable procedures.
The need for specific microbiological or preservation efficacy tests should be determined according to the product's formulation, characteristics, and risk profile.
8. Evaluating Packaging Compatibility
Packaging is sometimes overlooked during discussions of cosmetic stability.
Yet consumers do not purchase a formulation in isolation.
The product and its packaging together form a complete system.
ISO/TR 18811 considers packaging interactions as part of stability evaluation.
The Cosmetics Europe guidelines also recommend examining both the effects of packaging on the product and the effects of the product on its packaging.
Packaging may influence:
Light transmission
Exposure to air
Moisture loss
Retention of volatile constituents
Conversely, the cosmetic product may interact with the packaging materials over time.
This is not merely a theoretical concern for rose water.
In a study examining Rosa damascena rose water samples, dibutyl phthalate was detected in some samples.
The researchers discussed the possibility that this substance may have migrated from packaging materials into the samples.
This observation illustrates why product–packaging compatibility deserves scientific attention.
Whenever possible, stability evaluation should therefore be conducted using, or otherwise appropriately linked to, the actual packaging system intended for commercial distribution.
What Is Accelerated Stability Testing?
Waiting several years before introducing a cosmetic product to the market is not always practical.
For this reason, accelerated stability testing is widely used during cosmetic product development.
In an accelerated study, the product is exposed to controlled conditions that may be more demanding than those normally encountered during everyday use.
The objective is to observe certain changes within a shorter period.
Elevated temperatures are one example of conditions that may be used.
According to Cosmetics Europe, a good practice is to support predictions obtained from accelerated stability studies with periodic monitoring of reference samples stored at ambient temperature after market introduction.
An Important Scientific Limitation
Accelerated stability testing is not the same as real-time stability testing.
For example, if a product remains stable for several months at an elevated temperature, this finding does not automatically justify the conclusion:
“This product will definitely remain stable for 10 years at room temperature.”
Accelerated testing can help predict product behaviour, but it does not provide an exact substitute for long-term observations under normal storage conditions.
Real-time data are particularly valuable when evaluating long-term stability claims.
What Is Real-Time Stability Testing?
In a real-time stability study, the product is monitored over an extended period under its expected normal storage conditions.
This approach requires more time, but it provides direct evidence about how the product behaves under conditions representative of actual storage.
Real-time testing can help evaluate whether important product characteristics remain within defined acceptance criteria over time.
For this reason, accelerated and real-time stability studies should not necessarily be viewed as competing approaches.
They can serve as complementary tools within a comprehensive stability evaluation programme.
Accelerated studies may help identify potential problems earlier, while real-time observations provide valuable evidence about long-term behaviour under normal conditions.
What Does It Mean When an Old Product Still Appears Unchanged?
Scientific terminology is particularly important when discussing long-term observations.
For example, imagine that a rose water product manufactured several years ago still appears:
Clear
Normal in fragrance
Unchanged in colour
This is a valuable long-term observation.
However, it is not, by itself, equivalent to a controlled stability study.
If the older sample is also examined through laboratory measurements of pH, microbiological quality, and relevant chemical characteristics, the resulting evidence becomes considerably stronger.
Nevertheless, such findings should not automatically be described as a prospectively planned real-time stability study.
A formally designed real-time study generally involves predefined storage conditions, testing intervals, analytical methods, and acceptance criteria established at the beginning of the study.
An essential part of scientific credibility is accurately describing the nature and limitations of the evidence available.
Can Rose Water Without Added Preservatives Remain Stable?
Broad generalizations should be avoided.
The statement:
“A product without preservatives must spoil quickly.”
is not scientifically accurate as a universal rule.
Similarly, the statement:
“A natural product cannot spoil because it is natural.”
is also incorrect.
A product's stability may be influenced by numerous factors, including:
Manufacturing method
Characteristics of the raw materials
Chemical composition
pH
Manufacturing hygiene
Initial microbiological quality
Filling procedures
Packaging
Storage conditions
Therefore, the appropriate way to determine whether a rose product without added preservatives is stable is not to rely on assumptions, but to evaluate the product through suitable testing methods.
Any conclusions should be based on the characteristics and results of the specific product examined.
How Does Stability Testing Relate to Shelf Life?
Stability and shelf life are closely related concepts, but they are not identical.
The FDA generally descri