An Evidence-Based Guide to Reformulation, Ingredient Substitution, Percentage Adjustments, Emulsion Stability and Botanical Extract Compatibility

Madabuzz Knowledge Hub | DIY Lab | Deep Dive | Part 1 of 3

A cosmetic formula can look deceptively simple on paper.

Water, oils, emulsifiers, humectants, preservatives and botanical extracts are listed as percentages. Everything adds up to 100%, and the instructions explain how to combine the ingredients.

Then you decide to change something.

Perhaps you want a lighter face cream, a less sticky serum or a higher percentage of a botanical extract. Maybe an ingredient is unavailable, or you want to replace one oil with another.

You change the number in the formula, adjust the water to keep the total at 100%, and prepare the batch.

At first, everything looks fine.

A few days later, the cream separates. The viscosity changes. The botanical extract forms a haze. Or the product still looks normal, but its preservative system has not been evaluated under the new conditions.

What happened?

The problem is that a cosmetic formula is not simply a list of ingredients that add up to 100%. It is a physical and chemical system in which ingredients, concentrations and processing conditions interact.

Changing one component can influence several others.

This guide explains how to modify cosmetic formulas systematically, distinguish simple percentage adjustments from genuine reformulation, evaluate ingredient substitutions and recognise when a change requires additional stability or safety testing.

Throughout the article, we will use Acmella oleracea extracts as an example of why botanical ingredient additions require more thought than simply increasing an active ingredient percentage.

1. What Does It Mean to Adjust a Cosmetic Formula?

Adjusting a cosmetic formula means deliberately changing its composition, processing conditions or both to achieve a particular objective.

That objective might be:

• Improving texture or spreadability.

• Reducing stickiness.

• Changing viscosity.

• Incorporating a new botanical extract.

• Replacing an unavailable ingredient.

• Adjusting the oil-to-water ratio.

• Modifying the sensory experience.

• Addressing a stability problem.

• Adapting a formula to a different packaging format.

Not all adjustments have the same level of complexity.

1.1. A minor numerical adjustment

Suppose a formula contains 3% glycerine.

You want to test a version containing 2.5%.

You reduce glycerine by 0.5 percentage points and increase water by the same amount.

The formula still totals 100%.

This is a straightforward mathematical change, but it may still influence skin feel, water activity, viscosity or preservative performance.

1.2. A functional ingredient adjustment

Suppose you increase an emulsifier from 3% to 4%.

This may influence the emulsion's physical structure, viscosity, sensory properties and stability.

The outcome depends on the emulsifier system and the other ingredients.

1.3. A material substitution

Suppose you replace one emulsifier with another.

Even if both are described as emulsifiers, they may have different chemical structures, processing requirements and formulation behaviour.

A direct one-for-one substitution may not be appropriate.

1.4. A formulation-system change

Suppose you convert an oil-in-water cream into a water-free balm.

This is not a minor adjustment.

It changes the product's physical structure, ingredient requirements and potentially its preservation strategy.

1.5. The key principle

The more a change affects an ingredient's function or the structure of the product, the more it should be treated as a new formulation development exercise.

2. Why Cosmetic Formulas Are Interconnected Systems

A cosmetic formula is made up of ingredients that interact physically and sometimes chemically.

Consider a typical oil-in-water cream.

It may contain an aqueous phase, an oil phase, emulsifiers, viscosity modifiers, preservatives and functional additives.

Each component influences the behaviour of the finished product.

2.1. The aqueous phase

The aqueous phase may contain water-soluble humectants, salts, botanical extracts and other ingredients.

Changes can influence solubility, ionic strength, viscosity and the environment in which preservatives operate.

2.2. The oil phase

The oil phase may contain emollients, waxes, fatty alcohols and oil-soluble ingredients.

Changes can affect texture, spreading behaviour and the demands placed on the emulsifier system.

2.3. The emulsifier system

Emulsifiers help stabilise the interface between oil and water phases.

Their performance depends on the overall formulation, not merely their own percentage.

2.4. The viscosity system

Thickeners and rheology modifiers influence how a product flows and behaves under stress.

Some are sensitive to pH, electrolytes or processing conditions.

2.5. The preservative system

Preservative performance can depend on concentration, pH, water activity, ingredient interactions, packaging and other factors.

A formulation change may influence these conditions.

2.6. The botanical extract system

Botanical extracts may introduce carrier solvents, dissolved solids, pigments, salts and other constituents.

Their effects depend on the specific extract.

2.7. Why these connections matter

An adjustment intended to improve one property may unintentionally change another.

For example, increasing an extract carried in glycerine may increase the total glycerine contribution and alter the product's sensory properties.

The formula may still total 100%, but its behaviour can change.

3. The First Rule: Define What You Want to Improve

Before modifying a formula, identify the problem or objective.

A vague goal such as “make the cream better” is difficult to test.

A specific objective is easier to evaluate.

3.1. Examples of useful objectives

3.2. Why a defined objective matters

Without a clear objective, it becomes difficult to determine whether the adjustment succeeded.

3.3. Change the minimum necessary

A useful experimental approach is to change only what is needed to investigate the chosen objective.

This reduces the number of possible explanations for a different result.

3.4. Not every objective can be judged visually

A cream may look smoother without being more stable.

A serum may feel lighter without delivering an ingredient differently.

A product may remain visually unchanged while its preservative efficacy changes.

3.5. The practical lesson

Define the desired result and the method used to evaluate it before preparing the revised formula.

4. Understanding the 100% Rule

Most cosmetic formulas are expressed as percentages by mass.

The total should equal 100%.

Where \(p_i\) represents each ingredient's percentage.

4.1. Example formula

The following is a simplified mathematical illustration, not a validated or recommended cosmetic recipe.

4.2. Increasing one ingredient

Suppose the botanical extract is increased from 1% to 2%.

That is an increase of one percentage point.

If water is the designated adjustable component, water may be reduced from 75% to 74%.

The revised formula still totals 100%.

4.3. The mathematical result

4.4. What this proves

The revised formula is mathematically consistent.

4.5. What it does not prove

It does not prove that:

• The extract is compatible at 2%.

• The emulsion remains stable.

• The preservative system remains adequate.

• The pH remains suitable.

• The product is safe.

• The extract provides greater efficacy.

A formula totalling 100% is necessary for percentage-based composition calculations, but it is not evidence of formulation stability or safety.

5. Percentage Points vs Relative Percentage Changes

One of the most common formulation calculation errors is confusing percentage points with relative percentage changes.

5.1. Example

An ingredient increases from 1% to 2%.

The absolute difference is:

The relative increase is:

The ingredient concentration has doubled.

5.2. Another example

An ingredient decreases from 5% to 4%.

The absolute difference is one percentage point.

The relative decrease is:

5.3. Why the distinction matters

A one-percentage-point change can be substantial for an ingredient originally used at a low concentration.

5.4. Low-percentage ingredients

Increasing an ingredient from 0.1% to 0.2% is a 100% relative increase.

That may be important for ingredients with narrow concentration ranges.

5.5. Practical documentation

Record both the original and revised percentages.

When describing the magnitude of a change, distinguish between percentage points and relative percentage differences.

6. Interactive Formula Adjustment Calculator

Use this calculator to see how increasing or decreasing an ingredient affects the designated adjustable component, usually water.

7. Why Water Is Often Adjusted, but Not Always

In many water-containing cosmetic formulas, water is listed as the ingredient used to bring the total to 100%.

This is sometimes written as water q.s. to 100%.

The abbreviation q.s. means quantity sufficient.

7.1. Why water is convenient mathematically

Water often represents a large fraction of the formula.

A small adjustment to another ingredient can therefore be balanced by changing the water percentage.

7.2. Why water is not an inactive placeholder

Water influences:

• Solvent properties.

• Product viscosity.

• Ingredient concentrations.

• Water activity.

• The environment relevant to microbial growth.

• Processing behaviour.

7.3. Example

Increasing glycerine from 3% to 6% and reducing water by three percentage points keeps the total at 100%.

But the product may become noticeably more tacky.

7.4. Another example

Replacing part of the water with a botanical extract carried in ethanol can introduce a solvent that was not previously present.

The resulting formula is not equivalent to one containing the same mass of pure water.

7.5. When water adjustment is inappropriate

Water should not automatically be used to compensate for a change that requires restructuring the oil phase, emulsifier system or other functional components.

7.6. The central lesson

Water is often a convenient balancing component, but adjusting water does not neutralise the physical or chemical consequences of changing another ingredient.

8. The Difference Between Ingredient Percentage and Active Concentration

This distinction is especially important for botanical extracts.

An extract may contain an active or marker compound at a concentration much lower than 100%.

8.1. Example: Acmella extract

Suppose a hypothetical Acmella oleracea extract has a supported spilanthol concentration of 4% by mass.

The formula contains 1% of the extract.

The theoretical spilanthol concentration is:

8.2. Increase the extract to 2%

The theoretical spilanthol contribution doubles.

8.3. What else increases?

Increasing the extract may also increase the amount of its carrier and other constituents.

8.4. Why this matters

A formulation adjustment cannot be evaluated solely by looking at one selected compound.

8.5. Does doubling spilanthol double the skincare effect?

Not necessarily.

Dose-response relationships depend on the endpoint, formulation, exposure and supporting evidence.

8.6. What if the extract assay is unknown?

Theoretical spilanthol concentration cannot be calculated reliably from extract mass alone.

8.7. Practical conclusion

When adjusting botanical extract levels, distinguish the extract percentage from the concentration of any specific constituent.

9. Why One-for-One Ingredient Substitution Is Risky

Two ingredients may appear to serve the same purpose without behaving identically.

9.1. Carrier oils

Two oils can differ in fatty acid composition, viscosity, oxidation behaviour and sensory properties.

9.2. Emulsifiers

Two emulsifiers may have different processing requirements, phase preferences and compatibility profiles.

9.3. Humectants

Two humectants can differ in viscosity, sensory properties and interactions with other ingredients.

9.4. Thickeners

Different thickeners can respond differently to pH, electrolytes and shear.

9.5. Preservatives

Preservatives cannot be exchanged solely because they are marketed for the same purpose.

Their effectiveness depends on the actual formulation and use conditions.

9.6. Botanical extracts

Two Acmella oleracea extracts may differ in carrier, solids content, spilanthol assay and other characteristics.

9.7. The substitution question

Instead of asking:

Can I replace ingredient A with ingredient B at the same percentage?

Ask:

Which functions does ingredient A perform, and does ingredient B provide those functions under the conditions of this formula?

10. How to Evaluate an Ingredient Before Substitution

A systematic comparison reduces the risk of overlooking important differences.

10.1. Confirm identity

Check the ingredient's actual identity, not just its marketing name.

For cosmetic ingredients, INCI information can be useful, although an INCI name alone does not establish equivalence between commercial raw materials.

10.2. Review composition

Determine whether the material is a single substance, blend, dispersion or extract.

10.3. Review physical form

Is it a liquid, powder, paste, wax or other material?

10.4. Review solubility or dispersibility

Does it belong in the aqueous phase, oil phase or another preparation step?

10.5. Review concentration

Is the supplied material diluted in a carrier?

10.6. Review pH compatibility

Does the ingredient have a suitable operating pH range?

10.7. Review processing conditions

Does it require heating, cooling, hydration or a particular addition order?

10.8. Review stability information

Consider relevant sensitivity to heat, oxygen, light and other conditions.

10.9. Review safety and regulatory requirements

A replacement must be appropriate for the intended cosmetic product and market.

10.10. Review supporting documentation

Relevant sources may include technical data sheets, specifications, safety data sheets, certificates of analysis and supplier formulation guidance.

Each document answers different questions and has its own limitations.

11. Why Changing the Oil Phase Can Destabilise a Cream

An oil-in-water emulsion contains oil droplets dispersed in a continuous aqueous phase.

Its physical stability depends on the complete formulation and processing system.

11.1. Changing oil percentage

Increasing the oil phase may change droplet packing, viscosity, sensory properties and emulsifier requirements.

11.2. Changing oil identity

Different oils may interact differently with the emulsifier system.

11.3. Changing waxes or fatty alcohols

These ingredients may contribute to viscosity and internal structure.

11.4. Changing multiple oil-phase ingredients

Several simultaneous changes can make it difficult to identify why a product behaves differently.

11.5. The emulsifier is not a universal guarantee

An emulsifier that works in one formulation may not perform identically after the oil phase changes.

11.6. Example

A cream contains 10% oil.

Increasing the oil phase to 20% while leaving every other functional ingredient unchanged may significantly alter the emulsion.

11.7. What should be evaluated?

Relevant observations may include:

• Separation.

• Droplet structure, where appropriate equipment is available.

• Viscosity and rheological behaviour.

• Appearance.

• Behaviour under defined storage conditions.

11.8. Practical conclusion

A substantial oil-phase change should be treated as an emulsion reformulation, not merely a percentage correction.

12. Why Changing the Emulsifier Is More Than a Simple Swap

Emulsifiers differ in chemical structure and performance.

12.1. Different emulsification systems

Some emulsifiers are used in oil-in-water systems, others in water-in-oil systems, and some may support multiple applications depending on formulation conditions.

12.2. Different usage ranges

Supplier recommendations may differ.

12.3. Different processing requirements

Some emulsifying systems require particular temperatures or mixing conditions.

12.4. Different texture contributions

Certain commercial emulsifying blends contain fatty alcohols or other components that influence viscosity and sensory properties.

12.5. Different electrolyte tolerance

Some systems are more sensitive to salts and charged ingredients.

12.6. Different pH behaviour

Compatibility can depend on the formulation's pH.

12.7. Why equal percentages are not equivalent

Replacing 4% of one emulsifier with 4% of another does not guarantee equivalent emulsion structure or stability.

12.8. Practical approach

Treat an emulsifier replacement as a development change requiring review of the whole system, processing method and relevant stability performance.

13. Why Thickeners Can Be Sensitive to Small Changes

Thickeners and rheology modifiers influence how cosmetic products flow, spread and remain physically stable.

13.1. pH sensitivity

Some thickening systems change viscosity when pH changes.

13.2. Electrolyte sensitivity

Certain polymers respond strongly to dissolved salts.

13.3. Hydration requirements

Some materials require a defined hydration process.

13.4. Mixing sensitivity

High shear may affect the structure of certain thickening systems.

13.5. Ingredient interactions

Solvents, surfactants and other components may influence viscosity.

13.6. Botanical extract example

A botanical extract may introduce electrolytes or carrier solvents that alter a thickener's behaviour.

13.7. Why appearance can be misleading

A serum may appear stable immediately after mixing but become thinner or develop sediment during storage.

13.8. Practical conclusion

When a formula becomes thinner or thicker after an ingredient change, investigate the full system rather than automatically adding more thickener.

14. Why Preservative Changes Require Particular Care

Preservatives help control microbial contamination in susceptible cosmetic products.

Their effectiveness depends on more than the amount added.

14.1. Concentration

The preservative must be used within appropriate conditions and applicable restrictions.

14.2. pH

Some preservatives have pH-dependent effectiveness.

14.3. Solubility and distribution

A preservative must be appropriately distributed in the formulation.

14.4. Ingredient interactions

Other components may influence preservative availability or performance.

14.5. Packaging

Product exposure during use can influence contamination risk.

14.6. Water activity

Water activity is relevant to microbial growth, but it is not interchangeable with water content.

14.7. Why a formula adjustment matters

Changing water, humectants, botanical extracts or other ingredients can affect the environment in which the preservative system operates.

14.8. Preservative challenge testing

Appropriate preservative efficacy testing may be necessary to evaluate a formulation.

14.9. Practical conclusion

A preservative system should not be assumed adequate in a revised formula simply because its percentage remains unchanged.

15. Botanical Extract Substitution: Why the Carrier Matters

Botanical extracts are often described by their plant source.

However, the supplied commercial material may include carrier substances and other formulation-relevant components.

15.1. Example

Consider two hypothetical Acmella oleracea extracts.

Extract A is supplied in an oil-based carrier.

Extract B is supplied in a glycerine-water carrier.

15.2. Are they interchangeable?

Not automatically.

They may differ in:

• Solubility and phase compatibility.

• Viscosity.

• Water contribution.

• Oil contribution.

• Spilanthol assay.

• Other constituent profiles.

• Processing requirements.

15.3. Equal extract percentages

Adding 2% of Extract A and 2% of Extract B does not necessarily introduce equivalent amounts of spilanthol or equivalent carrier systems.

15.4. Why the difference matters

An oil-based extract may influence the oil phase.

A glycerine-water extract may influence the aqueous phase and humectant balance.

15.5. The correct comparison

A meaningful comparison should consider the complete supplied material, not only the botanical name.

15.6. Practical conclusion

Botanical substitution is a formulation change and an ingredient-quality comparison at the same time.

16. When Does an Adjustment Become a New Formula?

There is no universal percentage threshold that determines when an adjustment becomes a completely new formulation.

The significance depends on the change.

16.1. Small changes can be important

A small adjustment to a preservative, pH-sensitive ingredient or concentrated active may have substantial implications.

16.2. Large changes can alter the system

Increasing an oil phase or replacing an emulsifier can change the product's physical structure.

16.3. Supplier changes can matter

A new raw-material supplier may provide a material with different specifications or performance characteristics.

16.4. Processing changes can matter

A formula prepared at a different temperature or with different mixing equipment may behave differently.

16.5. Packaging changes can matter

A product packaged in a jar may experience different use-related exposure than one in a pump or airless container.

16.6. The practical definition

A change should be treated as significant when it could affect a critical quality attribute, product safety, regulatory compliance or the validity of existing supporting evidence.

16.7. What to do

Document the change, assess its potential effects and determine what testing or review is needed.

17. A Practical Formula Change-Control Record

Even small laboratories benefit from documenting formulation changes.

A simple change-control record might include:

17.1. Why version numbers matter

Without version control, it can become difficult to determine which formula produced a particular result.

17.2. Why the reason matters

A change should have a clear purpose.

17.3. Why risks should be recorded before testing

This helps ensure that the evaluation is not limited to whether the revised product looks attractive.

17.4. Why observed results matter

The actual result may differ from the expected effect.

17.5. Practical conclusion

A good formulation record preserves both the calculation and the reasoning behind the change.

18. The One-Variable-at-a-Time Approach

Changing one variable at a time can make early formulation experiments easier to interpret.

18.1. Example

Suppose a cream feels too greasy.

Possible changes include:

• Reducing the oil percentage.

• Replacing one emollient.

• Changing the emulsifier system.

• Modifying the viscosity system.

Changing all four at once makes it difficult to identify which change produced the result.

18.2. A simpler experiment

Prepare a revised version with one defined change.

Keep other ingredients and processing conditions as consistent as practical.

18.3. Record the outcome

Compare the revised formula with the original using defined observations.

18.4. Limitations

One-variable-at-a-time testing does not efficiently reveal every interaction between formulation variables.

More structured experimental designs may be appropriate for complex development.

18.5. Why it remains useful

For early-stage DIY formulation, controlled single-variable changes can improve understanding and reduce unnecessary complexity.

18.6. Practical principle

Change deliberately, record precisely and evaluate the result before making the next adjustment.

19. Common Formula Adjustment Mistakes

Mistake 1: Increasing an ingredient without reducing another component.

The formula no longer totals 100%.

Mistake 2: Assuming a 100% total proves the formula is correct.

Mathematical consistency does not establish compatibility or safety.

Mistake 3: Replacing ingredients based only on their marketing category.

Two emulsifiers, oils or botanical extracts may behave differently.

Mistake 4: Ignoring the carrier in a botanical extract.

The carrier contributes to the final formula.

Mistake 5: Increasing an active ingredient without reviewing its use conditions.

Higher concentration does not automatically mean greater benefit or acceptable safety.

Mistake 6: Changing several variables at once.

The result becomes harder to interpret.

Mistake 7: Assuming visual stability proves microbiological stability.

A product can look normal while presenting microbiological concerns.

Mistake 8: Ignoring pH after a change.

Some ingredients and systems are pH-sensitive.

Mistake 9: Reusing the original stability evidence without review.

A revised formulation may require additional evaluation.

Mistake 10: Failing to record the exact changes.

Without documentation, results become difficult to reproduce.

20. Part 1 Summary

Adjusting a cosmetic formula is not simply an exercise in changing percentages.

Every modification should begin with a defined objective and an understanding of the affected formulation system.

The key lessons are:

• A cosmetic formula is an interconnected physical and chemical system.

• A total of 100% confirms mathematical consistency, not stability or safety.

• Percentage-point changes and relative percentage changes must be distinguished.

• Water is often the balancing component, but it is not chemically irrelevant.

• Ingredient substitutions require evaluation of identity, composition, function and compatibility.

• Changes to oils, emulsifiers and thickeners may affect emulsion structure and viscosity.

• Preservative performance cannot be assumed unchanged after reformulation.

• Botanical extracts contribute carrier materials as well as plant-derived constituents.

• Increasing an Acmella oleracea extract changes its theoretical constituent contribution but does not establish greater efficacy.

• Version control and change records make formulation experiments easier to interpret.

The central principle: Change one thing with a clear purpose, but evaluate everything that change could affect.

Coming in Part 2

How to Reformulate Creams, Serums and Botanical Extract Formulas Step by Step

Part 2 will cover practical reformulation scenarios, including how to reduce greasiness, adjust humectants, change oil phases, incorporate Acmella extracts with different carriers, evaluate pH changes and troubleshoot emulsions that become too thin, too thick or unstable.

We will also work through complete before-and-after formula tables, showing how to preserve a 100% mass balance while identifying the scientific checks that mathematics alone cannot provide.