Ingredient guides
Understanding pH
pH is one of the most important — and most misunderstood — parts of cosmetic formulation. Even a well-designed formula can become unstable, irritating, ineffective, or difficult to preserve if the pH is not properly adjusted.
Understanding pH helps formulators create products that feel better on skin, remain stable over time, and support ingredient performance more effectively.
In this guide, we’ll explain what pH means in cosmetic formulation, why it matters, and how beginner formulators can work with pH more confidently.
What is pH?
pH measures how acidic or alkaline a formulation is. The pH scale runs from 0 to 14:
- Below 7 = acidic
- 7 = neutral
- Above 7 = alkaline
Most skincare formulations sit between pH 4.5 and 6.5 because this range generally aligns better with the skin’s natural surface environment.
Why pH matters
pH influences preservative performance, ingredient stability, viscosity, surfactant mildness, and overall skin compatibility.
Why pH matters in cosmetic formulation
Many cosmetic ingredients only function properly within specific pH ranges.
For example:
- Carbomer requires neutralisation to build viscosity
- Some preservatives perform poorly outside their effective pH range
- Niacinamide formulas are generally more stable in mildly acidic systems
- AHAs require lower pH ranges to remain active
Ignoring pH can result in:
- Thin or unstable emulsions
- Preservative failure
- Texture instability
- Increased irritation potential
- Ingredient degradation
How formulators measure pH
The most reliable way to measure cosmetic pH is with a properly calibrated digital pH meter.
While pH strips can provide rough guidance, they are generally less accurate for professional formulation work.
Typical skincare pH ranges
- Facial cleansers: pH 5–6
- Hydrating serums: pH 5–6
- Creams and lotions: pH 5–6
- AHAs/exfoliants: often pH 3–4
How to adjust pH
Formulators typically use acidic or alkaline materials to adjust finished formulations.
Common pH adjusters include:
- Lactic Acid
- Citric Acid
- Sodium Hydroxide solutions
Small adjustments are usually made slowly while mixing and re-testing.
pH and preservative systems
Preservative systems are heavily affected by pH.
Ingredients such as sodium benzoate and potassium sorbate are significantly more effective in acidic formulations, while other systems perform across broader pH ranges.
This is why pH and preservation should always be considered together rather than separately.
Learn more in our guide to Understanding Preservatives & Chelators in Cosmetic Formulation.
pH and thickening systems
Some thickening systems depend on pH for proper viscosity development.
Carbomer is one of the best-known examples. Without neutralisation, carbomer dispersions remain thin and watery.
Explore this further in Understanding Thickeners & Gelling Agents in Cosmetic Formulation.
Common beginner mistakes with pH
- Not checking final pH after adding preservatives
- Adjusting pH too aggressively
- Using inaccurate pH strips
- Ignoring ingredient-specific pH requirements
- Failing to re-check pH after 24 hours
Final thoughts
Understanding pH is one of the biggest steps toward becoming a more confident formulator. Even simple awareness of pH behaviour can dramatically improve stability, texture, preservation, and overall product performance.
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