What Is a “Substance” Under REACH?

A Simple Guide to Understanding Substance Identity

After learning what REACH is and whether it applies to your company, the next big question is:

“What exactly is my substance?”

This may sound simple, but in REACH, correctly identifying your substance is one of the most important steps. Many companies face problems not because they lack data — but because they misunderstand what their substance actually is.

Let’s break it down in an easy way.

Why Is Substance Identity So Important?

REACH registration is based on substances, not products.

Before registering, a company must clearly know:

• What chemical it is

• What it contains

• How it is made

• Whether it is the same as substances registered by other companies

If the substance identity is wrong:
Registration can be rejected
Extra testing may be required
Compliance risks increase

So this step comes before everything else.

What Does REACH Mean by “Substance”?

In simple terms, a substance is a chemical material that has a defined chemical composition.

It includes:
✔ The main chemical(s)
✔ Small unwanted chemicals formed during manufacturing (impurities)
✔ Chemicals added to keep it stable (additives)

It does not include:
Solvents that can be removed without changing the substance

Substance vs Mixture vs Article (Very Important!)

Many beginners confuse these.

TermWhat It MeansExampleSubstanceOne chemical materialEthanol, AcetoneMixtureBlend of two or more substancesPaint, detergentArticleAn object where shape/design matters more than chemistryPen, chair, mobile phone

Even if you sell a mixture or an article, REACH rules usually apply to the substances inside them.

Different Types of Substances Under REACH

Not all substances are “pure.” REACH recognizes three main types.

A. Mono-constituent Substance

Contains one main chemical (usually more than 80%).

Example: High-purity acetone.

B. Multi-constituent Substance

Contains two or more main chemicals in significant amounts.

Example: A reaction that produces two main isomers.

C. UVCB Substance

This stands for:

Unknown or Variable composition, Complex reaction products, or Biological materials.

These are more complex substances where:

• Many components are present, or

• Exact composition is not fully known

Examples:

• Petroleum fractions

• Plant extracts

• Complex reaction products

These are common in industry and often harder to register.

What Is “Substance Sameness”?

Under REACH, companies registering the same substance must work together.

To check if substances are the same, companies compare:

• Chemical name

• CAS / EC number

• Composition

• Manufacturing process

• Laboratory data (analytical results)

If substances are not considered the same, they cannot share the same registration.

Why Can This Be Difficult?

Substance identification becomes tricky when:

• Composition changes from batch to batch

• The material is complex (UVCB)

• Impurity levels differ

• The process changes

This is why good analytical data is important.

Simple Real-Life Examples

Example 1:
95% ethanol with 5% water → Substance

Example 2:
Cleaner containing ethanol + perfume + surfactant → Mixture

Example 3:
Plastic toy → Article, but plastic contains substances

How Do Companies Define a Substance for REACH?

Companies usually collect:

• Chemical name

• Composition details

• Structure information

• Lab analysis data

• Description of manufacturing process

This information is entered into IUCLID for registration.

Why This Step Comes First

Substance identity affects:

• Data requirements

• Costs

• Data sharing

• Legal compliance

Without correctly defining your substance, REACH registration cannot move forward properly.

Final Takeaway

Before asking:

“What data do I need?”
You must first ask:

“What exactly is my substance?”

Getting this right is the foundation of REACH compliance.