Is your product a substance or mixture

For CLP-classifiable products, the key distinction is whether a product is a substance, or a mixture.  This assessment gives you different routes for classification.

Substances are defined under CLP, Article 2, Definitions, item 7, as: “a chemical element and its compounds in the natural state or obtained by any manufacturing process, including any additive necessary to preserve its stability and any impurity deriving from the process used, but excluding any solvent which may be separated without affecting the stability of the substance or changing its composition

Mixtures are defined under CLP, Article 2, Definitions, item 8 as: “a mixture or solution composed of two or more substances“.

Substances and mixtures can have many different physical formats:

  • solids, e.g. in massive form (like a bar of steel), or in powder form (like a powdered chemical such as sodium carbonate)
  • liquids
  • gases
  • gels
  • pastes

ECHA provide guidance on identifying and naming substances for REACH and CLP, current version 2.1, May 2017 .


Articles are different from solid substances or mixtures.  An article is defined under CLP, Article 2, Definitions, Item 9, as “an object which during production is given a special shape, surface or design which determines its function to a greater degree than does its chemical composition are considered to be articles“.  For example, a bar of steel which is made into a kitchen knife becomes an article.

Articles can, of themselves, contain classifiable substances or mixtures, which may or may not be intended to be released; and this can mean that they need to be classified, on the basis of the material which is being released.  For more information, see: .

UVCB substances

Substances are often considered to be pure compounds or elements, but in the real world they may contain impurities, or even be a mixture of individual substances which is convenient to treat as a substance.  This concept is given a name in REACH as UVCB, Unknown Variable Complex Biological substances, and is usually applied to organic materials like distillation fractions of oil; or essential oils, which are made by distilling flowers or other plant parts, and which contain multiple individual substances.

However, this complexity can also occur in inorganic products, e.g. a hydrogen fluoride urea complex (as discussed on the CHCS forum in 2017); or in manufactured products, e.g. chromic acid solution, where adding a single substance, chromium trioxide, to water, produces a solution containing many individual substances.

The reason why it is important to decide whether your product is a substance or mixture is because it affects the classification method(s) you can use, either the first principles method for a substance; or the algorithm method for a mixture.

This will also have implications for REACH registration.  A single UVCB substance is one registration – a mixture will contain multiple substances, and may therefore require multiple REACH registrations (depending on the volumes per annum involved).

Mixtures can be made by different routes

Although not explained within CLP, mixtures can be produced either by mixing non-reactive components together (whether these are substances or mixtures), what is usually termed “formulation” in the UK chemical industry; or by reacting substances (or other mixtures) together in situ to create the new substances within the mixture, or “manufacture by reaction”.

For CLP, this distinction is meaningless, but in practical terms it is very important for manufacturers in the UK under other regulations:

  • making mixtures by formulation does not usually require an Environmental or IPPC Permit (although you should check the regulations to make sure); and, if you buy all of your raw materials within the EU, you are a Downstream User (DU) under REACH, and only have DU responsibilities (mainly to use the product in an approved way)
  • making new substances by reaction usually does require an Environmental or IPPC Permit, and will also require you to carry out a REACH registration for each new substance (if made at 1 tonne per annum or greater)

Sometimes formulators find themselves making new substances by reaction, which can take them into scope for both the Environmental Permit regulations and REACH.  One way to avoid this, is to work out what the new substances are, and formulate with them directly, although that can have implications for formulation purity and stability.


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