Aqua
Also known as Water, Eau, Purified Water, Distilled Water
“No regulator has issued a verdict on this ingredient.”
Water (INCI: AQUA, CAS 7732-18-5) is the most prevalent single ingredient in cosmetics, functioning as the primary solvent and continuous phase for the vast majority of leave-on and rinse-off formulations. No regulatory body has issued an ingredient-level safety verdict on water itself: CIR has not assessed water (verified absent from the September 2022 Quick Reference Table; CIR scopes its work to cosmetic ingredients with potential safety questions, and water has none); the EU CosIng database lists Aqua as a solvent with no Annex restriction (not directly verifiable in this session due to the JS-rendered SPA); SCCS has issued no opinion on water; FDA does not regulate water as a distinct cosmetic ingredient. Pharmacopoeial water grades (USP Purified Water <1231>, Water for Injection) exist as quality specifications for manufacturing inputs but are not safety verdicts for the finished cosmetic ingredient. The published cosmetic-science literature on water focuses on its role as a microbial growth substrate (water-based formulations require preservation, packaging engineering, or hurdle technology to remain microbiologically stable through use) and on water-quality inputs to manufacturing (mineral content, microbial bioburden of source water). The absence of an admissible regulatory verdict here is structural and correct: no jurisdiction has questioned water's safety, so no jurisdiction has affirmed it. This packet documents that absence honestly rather than fabricating coverage.
Universal solvent for hydrophilic actives (hyaluronic acid, glycerin, niacinamide, peptides, plant extracts), allowing efficient delivery in serums, toners, essences, and the aqueous phase of emulsions
Thermodynamically and biologically inert with respect to skin chemistry at use concentrations; the solvent that the human stratum corneum is best adapted to encounter
No documented systemic toxicity, sensitization, irritation, or carcinogenicity attributable to water as a cosmetic ingredient
Enables every emulsion (cream, lotion), every gel, every aqueous serum, and every rinse-off cleanser — functionally the single most important ingredient class in cosmetic chemistry
Water-based cosmetic formulations are inherently susceptible to microbial contamination (bacteria, yeast, mold) and require either chemical preservation, packaging-mediated protection (airless dispensers, single-use), low water activity (a_w < 0.8), or extreme pH to remain stable through consumer use — a quality issue tied to the product, not the water ingredient itself
Source-water mineral hardness (calcium, magnesium ions) can destabilize emulsions, interact with anionic surfactants and chelators, and complicate formulation reproducibility — manufacturers typically specify deionized, distilled, or USP-grade purified water to control this
Source-water bioburden (Pseudomonas aeruginosa, Burkholderia cepacia, and other water-system organisms) is a documented contamination vector for finished cosmetics; pharmacopoeial water specs and in-line filtration/UV treatment exist to control this at the manufacturing stage
No ingredient-level safety verdict from any of the five jurisdictions in this directory's scope (CIR, CosIng, SCCS, FDA, Prop65) — not because water is unsafe, but because no regulator has had reason to question it; the resulting INSUFFICIENT_DATA tier is a structural artifact, not a flag