The REACH regulation focuses exclusively on substances. To ensure a properly working REACH system, unambiguous substance identification is thus essential.

Substances within the scope of REACH

REACH concerns the manufacture, import, placing on the market and use of substances on their own, in preparations (intentional mixtures or solutions composed of two or more substances) and articles.
Preparations and articles as such are not regulated in REACH. Therefore, in order to meet the REACH provisions, and in addition to the inventory of substances on their own, manufacturers and importers have to list all the substances present in manufactured or imported preparations and articles.

This definition goes beyond a pure chemical compound defined by a single molecular structure.
Substances within the scope of REACH are typically the product of a chemical reaction in manufacture and may contain multiple distinct constituents. Substances, as defined in REACH, also include substances chemically derived or isolated from naturally occurring materials, which may comprise a single element or molecule (e.g. pure metals or certain minerals) or several constituents.

Some substances are exempted from REACH or from parts of REACH (for more information, see table Scope of the REACH regulation).

Various types of substances

For identification and naming in REACH, substances are divided into two main groups:

1. “Well defined substances”: substances with a defined qualitative and quantitative composition.
2. “UVCB substances”: substances of Unknown or Variable composition, Complex reaction products or Biological materials.

Variability of composition for well defined substances is specified by the upper and lower limits of the concentration range(s) of the main constituent(s). For UVCB substances, the variability is relatively large and/or unpredictable.

When a registration is required for a “well defined substance”, it shall include the substance chemical composition, the chemical identity and the content of each constituent in the substance. For some types of substances, the chemical composition alone is not enough for characterisation and some additional physical parameters about the chemical structures have to be added to the substance identification (e.g. crystallomorphology).

“UVCB substances” require other types of information for their identification in addition to what is known about their chemical composition because:

1. the number of constituents is relatively large and/or
2. the composition is, to a significant part, unknown and/or
3. the variability of composition is relatively large or poorly predictable.

When registration is required for an UVCB substance, manufacturers/importers shall include the name, the origin or source of the substance and the most relevant steps taken during processing. Other substance properties can also be important identifiers.

Rules for naming the various substances are given in diagram Identification and naming of substances.

Identifying equal substances

Manufacturers and importers have to determine if their respective substances may be regarded as the same for the purposes of REACH. The identification of equal substances is important in data sharing which allows for limited substance testing and is based on proper substance identification.

Grouping of structurally related substances

Under REACH, annexe XI opens the possibility of evaluating chemicals not on a one-by-one basis but by grouping chemicals in categories.
A chemical category is a group of chemicals whose physico-chemical and human health and/or environmental toxicological properties and/or environmental fate properties are likely to be similar or follow a regular pattern as a result of structural similarity (or other similarity characteristic). The use of a category approach will mean that it is possible to identify properties which are common to at least some members of the category. The approach also provides a basis to identify possible trends in properties across the category.
As a result, it is possible to extend the use of measured data to similar untested chemicals. Reliable estimates that are adequate for classification and labelling and/or risk assessment can therefore be made without further testing.