; and (ii) not later than 90 days after the close of such public comment period, approve or deny the petition. (C) If the Secretary approves a petition, the Secretary shall provide notice in the Federal Register of each addition made pursuant to such approval. (D) In denying a petition, the Secretary shall provide a written justification to the petitioner for the denial. (g) Guidance The Secretary— (1) shall, concurrently with the publication of the initial list under subsection (a), and upon adding any nonfunctional constituent pursuant to subsection (e) or (f) to the list under subsection (a), issue guidance for industry on best practices related to— (A) analytical testing for nonfunctional constituents in cosmetics and ingredients; and (B) detection limits; and (2) may periodically review and update such guidance. 624. Treatment of nonfunctional constituents A supplier of an ingredient or cosmetic shall— (1) not later than 1 year after a nonfunctional constituent is added to the list under section 623(a) pursuant to subsection (d), (e), or (f) of section 623, conduct testing for such nonfunctional constituent; and (2) prior to the sale of the ingredient or cosmetic to the brand owner, provide the brand owner a certificate of analysis that includes— (A) the levels of each such nonfunctional constituent present; (B) any analytical test used; (C) the detection limits of any analytical test used to detect each such nonfunctional constituent