Each substance registered or notified under the REACH or CLP Regulation needs an identifier in the submission tool REACH-IT. If a substance is not identified using an EC number, and it has not been previously registered or notified by any company, REACH-IT will automatically assign a new list number as an identifier to this substance. 

EC numbers originate from different pieces of historical legislation. Substances with EC numbers were considered as phase-in substances for REACH registrations. 

List numbers are purely technical identifiers that do not have any legal significance. This means that they should not be used, for example, in safety data sheets or other similar documents. 

EC and list numbers are used to ensure that registrations and notifications for one substance are consistently grouped and that they are carried together through regulatory processes. 

The EC and list numbers originate from the following sources: 

EC and list numbers historically share the same format of six numerical characters and one calculated check digit. 

As the list numbers in their current format will run out, the format will become alphanumerical. It will keep the same length but begin with a letter as the first character. Once all letters have been used as the first character, the second character will become a letter, and so on.  

Example of the current list number: 100-000-1
Example of the new list number: A00-001-5

List numbers assigned before the format change will stay as they are and will not be affected by the new format.