How to Test pH in Different Skincare Products

Understanding and testing the pH of your skincare products is an important part of making safe, stable and skin-friendly formulations.

Different products require different pH ranges, and the way you test the pH can also vary depending on whether you are testing a liquid, cream, gel or an anhydrous product.

What is pH?

pH measures how acidic or alkaline a water-based product is.

The pH scale generally ranges from 0 to 14:

Below 7: Acidic
7: Neutral
Above 7: Alkaline

Healthy skin has a naturally acidic surface, often referred to as the acid mantle. Many skincare products are therefore formulated within a mildly acidic range.

However, there is no single “correct” pH for every skincare product. The appropriate pH depends on the product, its ingredients, preservatives and intended use.

What Do You Need to Test pH?

For the most reliable results, use a calibrated digital pH meter.

You can also use pH test strips, but these are generally less accurate and can be difficult to read with coloured or opaque formulations.

If you use a digital pH meter:

Calibrate the meter according to the manufacturer’s instructions.
Use appropriate calibration solutions.
Rinse the electrode with distilled or deionised water.
Gently blot it dry.
Take your measurement.
Rinse the electrode again after testing.

Never simply place a dirty pH electrode into different products without cleaning it between tests.

How to Test Different Products

1. Lotions and Creams

Creams and lotions can be tested directly if they are sufficiently fluid for the electrode.

For thicker creams, prepare a small dilution.

A commonly used method is:

10 g product + 90 g distilled water = 10% dilution

Mix thoroughly and allow the mixture to become uniform before testing.

Insert the pH electrode into the sample and wait until the reading stabilises.

Record the result.

Important

The dilution method should be used consistently when developing and monitoring a formula. Do not compare a direct reading from one product with a diluted reading from another and assume the results are directly equivalent.

2. Facial Serums

Water-based serums are usually very easy to test.

Simply place a small amount into a clean container and insert the calibrated pH electrode.

Allow the reading to stabilise before recording it.

If the serum contains a lot of thickener or suspended material, a suitable dilution may provide a more practical measurement.

3. Gels

Products such as hyaluronic acid gels and carbomer gels can usually be tested directly.

Place enough gel into a clean container to allow the electrode to make good contact with the sample.

Avoid stirring aggressively, as this can introduce air bubbles and make the measurement less stable.

If the gel is extremely thick, a consistent dilution method may be necessary.

4. Shampoos and Body Washes

Shampoos, shower gels and body washes are generally water-based and can normally be tested directly.

Place the product into a clean beaker or container and allow excessive foam to settle.

Insert the electrode into the liquid portion of the sample.

Try not to measure a sample that is full of bubbles, as this can interfere with good contact between the electrode and the product.

5. Micellar Water and Toners

These are among the easiest products to test.

Place the product in a clean container and test directly using the calibrated pH meter.

Because these products are generally low-viscosity water-based formulations, a direct reading is usually straightforward.

6. Liquid Soap

Liquid soaps are usually alkaline because they are made using fatty acids and an alkaline ingredient such as potassium hydroxide.

Test the finished liquid soap directly if it is sufficiently fluid.

Remember that liquid soap does not need to have the same pH as a facial cleanser or lotion. Trying to force a true soap to a low, skin-friendly pH can destabilise the soap and may cause separation or other formulation problems.

7. Melt-and-Pour Soap

Melt-and-pour soap is not normally tested in the same way as a lotion or serum.

If you need to measure its pH, prepare a consistent aqueous sample rather than attempting to measure the solid soap bar directly.

A commonly used approach is to dissolve a measured amount of soap in distilled water and then measure the resulting solution.

The exact dilution should be kept consistent when comparing batches.

8. Cold Process Soap

Cold process soap is naturally alkaline.

Testing the surface of a solid soap bar with a pH meter is not an accurate method.

Instead, a measured amount of the soap can be dissolved or dispersed in distilled water using a consistent test method.

It is important to remember that pH alone does not determine whether a cold process soap is safe or properly made. Proper formulation, accurate weighing of sodium hydroxide, correct lye calculations and adequate curing are all essential.

9. Anhydrous Products

This is where many beginners make a mistake.

Products such as:

Body butters
Lip balms
Oil serums
Sugar scrubs containing no water
Lotion bars

do not have a meaningful pH because pH is a measurement of an aqueous system.

You cannot accurately measure the pH of pure oil by putting a pH strip or pH meter into it.

If a product contains no water, there is no aqueous phase in which conventional pH measurement can be performed.

What pH Should My Product Be?

There isn’t one universal pH that applies to all skincare products.

As a general formulation guide, many leave-on facial and body products are formulated somewhere around pH 4.5–6.0, while many rinse-off products may have different target ranges.

The correct target should always be determined by the individual formulation.

This is particularly important when using preservatives.

Why Is pH Important for Preservatives?

Many cosmetic preservatives have a specific pH range in which they work effectively.

Changing the pH of a formula can therefore affect the performance of the preservative.

For example, a preservative that works well at one pH may become significantly less effective outside its recommended range.

Always check the supplier’s technical information for:

Recommended usage rate
Effective pH range
Compatibility
Recommended processing temperature
Whether the preservative is suitable for your type of formulation

pH Testing Tips

For more reliable results:

Always calibrate your pH meter.

Use clean equipment.

Use distilled or deionised water when preparing dilutions.

Test the finished product rather than relying only on the pH of individual ingredients.

Allow the reading to stabilise before recording it.

Keep your testing method consistent from batch to batch.

Don’t adjust pH simply because a number “looks wrong”. Check what pH your particular formulation is designed to have.

How to Adjust pH

If your water-based formulation needs adjustment, small amounts of an appropriate acid or alkali solution can be added gradually.

For lowering pH, formulators commonly use a diluted acid solution such as citric acid or lactic acid.

For increasing pH, an appropriate diluted alkaline solution may be used.

Always add very small amounts, mix thoroughly and retest.

It is much easier to lower or raise pH gradually than to correct a product that has been dramatically over-adjusted.

A Simple Rule to Remember

Water-based product = pH can usually be measured.

Oil-only product = conventional pH measurement does not apply.

And remember:

pH testing is not the same thing as preservative testing or microbial testing.

A product can have a perfectly acceptable pH and still be microbiologically contaminated if it has not been properly formulated, preserved and manufactured.

Good formulation practice means considering pH, preservation, ingredients, packaging, manufacturing hygiene and stability together.

Testing your pH is a simple step that can make a big difference to the quality and consistency of your skincare products.

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