How We Calculate Cosmetic Biodegradability at The Today Project

“Biodegradable” is one of those words that appears everywhere in beauty.

But what does it actually mean when it is applied to a cosmetic formula?

At The Today Project, we believe environmental claims should be measurable. That is why, when we communicate the biodegradability of one of our formulas, we do not estimate it from the percentage of natural-origin ingredients, nor assume that a plant-derived ingredient is automatically biodegradable.

We look at the formula ingredient by ingredient, examine the available biodegradation data for each one, and calculate its contribution according to its concentration in the finished product.

It is a much less glamorous process than simply writing “biodegradable” on a bottle.

But it is a much more meaningful one.

Natural origin and biodegradability are not the same thing

This distinction is important.

Natural origin describes where an ingredient comes from or how it has been obtained. Biodegradability describes something different: what happens to that substance once microorganisms encounter it in the environment.

A formula can therefore have a very high percentage of ingredients of natural origin without that percentage automatically representing its biodegradability.

For the same reason, an ingredient does not necessarily have to be natural to be biodegradable.

At The Today Project, we treat these as two separate measurements.

When we want to understand biodegradability, we look specifically at biodegradation data.

So, how do we calculate the biodegradability of a cosmetic?

Our assessment starts with the complete quantitative formula.

Not simply the INCI list printed on the packaging, but the concentration of every ingredient in the finished product.

An independent laboratory then evaluates the biodegradability information available for the individual ingredients.

The methodology used for our assessment considers an organic ingredient biodegradable for the purpose of the calculation when it meets defined criteria for ready biodegradability, including testing consistent with OECD guidelines such as the OECD 301 or OECD 310 series, or equivalent evidence.

Evidence can also come from read-across to a structurally close analogue that has been demonstrated to be readily biodegradable.

Importantly, the methodology does not simply classify every positive-looking biodegradation result in the same way. Other statuses, such as substances calculated to be readily biodegradable or measured/calculated as inherently biodegradable, are not automatically counted as biodegradable in the percentage calculation.

That makes the calculation deliberately more selective.

Step 1: We examine every ingredient

Imagine a cosmetic formula as 100 pieces of a puzzle.

For each ingredient, we ask two questions:

How much of the formula does this ingredient represent?

and

What does the available evidence tell us about its biodegradability?

In the independent assessment performed on our Shampoo, Hand & Shower Gel, ingredients including Sodium C14-16 Olefin Sulfonate, Cocamidopropyl Betaine, Lauryl Glucoside, Coco-Betaine and Lauroyl/Myristoyl Methyl Glucamide were assessed individually.

The laboratory reviewed the biodegradation evidence associated with each ingredient rather than assigning one general environmental value to the finished formula.

Step 2: Readily biodegradable ingredients can contribute 100%

When a single-component organic ingredient or a homogeneous multi-component ingredient meets the methodology's criteria for ready biodegradability, it can be considered 100% biodegradable for the purpose of the formula calculation.

For example, the assessment assigned a biodegradability value of 100% to many of the ingredients in our Shampoo, Hand & Shower Gel.

But not every ingredient received 100%.

Cetrimonium Chloride, for example, was assigned 65% based on the available biodegradation data.

Sodium Citrate was assigned 97%, while Sodium Benzoate was assigned 60%.

For the fragrance in this particular assessment, no available biodegradability data were identified, so it was not simply assumed to be biodegradable.

That last point matters enormously to us.

No data should not automatically become 100%.

Step 3: Concentration matters

An ingredient present at 10% of a formula obviously has a different influence on the final result than an ingredient present at 0.01%.

That is why the biodegradability percentage is weighted according to the amount of each ingredient present in the formula.

In simplified terms, the laboratory takes:

the amount of each ingredient × its recognised biodegradability

and combines those contributions to determine the biodegradability of the formula.

The technical methodology expresses the calculation as a weighted relationship between the mass of biodegradable ingredients, their biodegradability percentage and the organic part of the formula.

So this is not a simple exercise in counting ingredients.

A formula containing nine biodegradable ingredients and one non-biodegradable ingredient is not necessarily “90% biodegradable.”

It depends on how much of each ingredient is actually present.

A simple example

Suppose, just for illustration, that a formula contained:

• 80% of an ingredient assessed as 100% biodegradable,

• 15% of an ingredient assessed as 80% biodegradable,

• and 5% of an ingredient for which no qualifying biodegradability contribution could be established.

The result would not be based on “two good ingredients out of three.”

It would be calculated according to their actual weight in the formula.

That distinction is fundamental.

Biodegradability is a property of the composition, not a marketing count of the INCI list.

What does 96.75% biodegradable actually mean?

This brings us to a real The Today Project example.

Our Shampoo, Hand & Shower Gel was independently assessed ingredient by ingredient.

The laboratory reviewed the quantitative composition and available biodegradability evidence and calculated:

Degree of biodegradability of the cosmetic product: 96.75%

That number therefore has a very specific meaning.

It is not the percentage of natural ingredients.

It is not the percentage of ingredients we personally consider “green.”

And it is not an estimate based on the origin of the raw materials.

It is the result obtained by applying a defined biodegradability methodology to the quantitative composition of the product.

Why OECD biodegradation tests matter

The methodology used in our assessment relies on recognised biodegradation criteria, including data from tests consistent with the OECD 301 and OECD 310 series.

These tests are used to assess ready biodegradability under defined conditions.

Having recognised criteria matters because otherwise the word “biodegradable” could mean almost anything.

A substance might eventually degrade under certain conditions, but that does not necessarily mean it meets the criteria to be considered readily biodegradable.

The methodology used for our assessment therefore distinguishes between different levels and types of biodegradation evidence rather than treating them as interchangeable.

Why we calculate instead of assume

For us, this is part of a larger principle at The Today Project:

environmental performance should be designed into a product and then measured wherever possible.

It is easy to choose ingredients because they sound natural.

It is more demanding to ask what happens to those ingredients after the product has been used.

This question becomes particularly relevant for products such as shampoos, shower gels and hand washes.

They are rinse-off products.

By design, they are used with water and eventually enter wastewater systems.

For our hotel amenities, where the same formulas can be used across many rooms and thousands of guest stays, understanding the environmental profile of the formula becomes even more relevant.

Biodegradable does not mean “disappears instantly”

There is another misconception worth addressing.

A biodegradability percentage should not be interpreted as saying that a product instantly disappears when it reaches water.

Biodegradation is a biological process involving microorganisms, and its behaviour depends on the substance and environmental conditions.

The methodology used in our assessment is based on established biodegradation evidence and defined criteria; it is not a claim that 96.75% of a shower gel vanishes the moment it goes down the drain.

That distinction is important when communicating environmental performance responsibly.

Biodegradability is not the same as aquatic safety

This may be the most important distinction of all.

A substance can be biodegradable and still have effects on aquatic organisms before it degrades.

Biodegradability tells us about degradation.

Ecotoxicology asks another question: what effects might a substance have on organisms in the environment?

That is why our environmental assessment does not stop at calculating biodegradability.

The same independent assessment of our Shampoo, Hand & Shower Gel also reviewed available ecotoxicological information for its ingredients, including aquatic toxicity data.

And that leads to another question we think cosmetic brands should be willing to ask:

What happens when our products reach marine ecosystems?

That is the subject of our next article.

Formulated with knowledge. Measured with evidence.

At The Today Project, we do not believe that better formulation comes from adding more ingredients.

It comes from understanding the ingredients we choose.

Where they come from matters.

What they do for the skin matters.

How much we use matters.

And what happens after they leave our skin matters too.

That is why, when you see a biodegradability percentage associated with one of our assessed formulas, there is a calculation behind that number.

Ingredient by ingredient. Percentage by percentage. Formula by formula.

Because responsible formulation should not begin with a claim.

It should begin with the evidence behind it.