Australian therapeutic sunscreens are multi-filter mixtures: Single-ingredient margin of safety assessment does not address cumulative exposure.

Australian sunscreens are regulated as therapeutic goods and recommended for daily whole-body application. Yet, the multi-filter formulations actually on sale have not previously been characterised at the population level. We extracted all therapeutic sunscreens with active AUST L designation from the Australian Register of Therapeutic Goods (ARTG) and analysed their UV filter combinations, concentrations and prevalence. After deduplication and removal of non-sunscreen items, 924 unique products remained. Of these, 187 (20.2%) were mineral-only sunscreens with no organic UV filter declared. The remaining 737 (79.8%) contained organic filters, all in combinations of two or more: 45.7% contained four organic filters, 85.2% four or more, and 39.5% five or more. Combined organic UV filter loads commonly reached 15-25% w/w of the total formulation. Twenty filter actives were identified; the market was dominated by avobenzone (641), octocrylene (600), octyl salicylate (411), homosalate (410) and zinc oxide (243). A targeted review of nine recurring organic filters identified three structural problems in the current single-ingredient Margin of Safety (MoS) assessment: shared endocrine targets, photochemical and oxidative-stress mechanisms that produce additive transformation products, and co-formulation with documented dermal penetration enhancers. None of these effects are summed across co-formulated filters in any current safety assessment. Non-dermal exposure pathways, including indoor air, indoor dust, human milk and chlorinated water, are likewise excluded. Single-ingredient MoS assessment does not account for cumulative exposure in these multi-filter products. The resulting cumulative risk remains uncharacterised. A pathway and mixture-based evaluation framework is feasible.