The European Union (EU) Cosmetics Regulation (EC) No. 1223/2009 requires companies to collect and assess reports of adverse health effects from the cosmetic products (undesirable effects) they market. Furthermore, undesirable effects that are considered as serious need to be reported to the national competent authorities. Cosmetics Europe, representing the European cosmetics industry, has developed these guidelines to promote a consistent practical approach for the management of undesirable effects and the notification of serious undesirable effects. Following these guidelines allows companies concerned to demonstrate due diligence and compliance with the legal requirements.