The European Chemical Regulation (EC) No. 1907/2006 (Registration, Evaluation and Authorisation of Chemicals, REACH) contains several obligations for industrial enterprises.
One of these obligations is the duty to communicate Substances of Very High Concern (SVHC) to the next commercial body according to Article 33. As per Article 33 „any supplier of an article containing such a substance in a concentration above 0.1 % weight by weight (w/w) shall provide the consumer with sufficient information, available to the supplier, to allow safe use of the article including, as a minimum, the name of that substance“.
Beside the manufacturer, also importers and distributors have to provide information within 45 days on SVHC on request by end consumers.
The current list of SVHC can be found at the website of the European Chemical Agency (ECHA):
https://echa.europa.eu/en/candidate-list-table
Sennheiser obviously complies with this obligation. Products that do contain SVHC substances are listed in the following report. Basically, Sennheiser puts forth an effort to have no SVHC in the products. With the legal deadlines latest, Sennheiser will substitute still existing SVHC.
Sennheiser products are safe for the user, also if SVHC should be part of the product. There are no safety instructions that have to be followed.
*A substance meeting the criteria in Article 57 and identified in accordance with Article 59(1).