The "Cosmetic Supply Chain Transparency Act of 2025" seeks to significantly enhance the safety of cosmetic products by amending Title VI of the Federal Food, Drug, and Cosmetic Act. This legislation introduces new subchapters focused on supply chain transparency and strengthens existing regulations. It clarifies that states retain the ability to implement requirements for greater transparency, disclosure, or protection regarding cosmetic ingredients and manufacturing practices, explicitly stating that the Modernization of Cosmetics Regulation Act of 2022 does not preempt such state actions. A core provision mandates that suppliers of cosmetics or ingredients must provide brand owners with comprehensive safety information upon request, including functions, hazards, chemical properties, and testing results for heavy metals and allergens. The bill also directs the Secretary of Health and Human Services to establish and maintain an FDA list of nonfunctional constituents known or expected to be present in cosmetics and harmful to human health or the environment. Suppliers are then required to conduct testing for these listed constituents and provide brand owners with a certificate of analysis detailing levels and test methods. Additionally, the Secretary gains authority to request supply chain information from any entity in cases of suspected adulterated or misbranded cosmetics, and the bill establishes civil penalties of up to $10,000 per day for violations of these new transparency and testing requirements.