The client challenge
A prestige cosmetics brand faced a California Proposition 65 matter involving titanium dioxide in pressed cosmetic powder products. The practical question was not simply whether TiO2 was present, but whether the test method matched the inhalation exposure pathway at issue. A bulk-material screen could identify the product's composition, but it would not necessarily show how much titanium dioxide was present in the respirable aerosol fraction.1,2,3
Public California materials identify the listed form as airborne, unbound titanium dioxide particles of respirable size. The current public fact sheet further limits the form on the Proposition 65 list to airborne particles measuring 10 micrometers or less. This distinction made particle-size separation central to the study design.2,3,4
The client faced product risk, legal exposure, reputational pressure, and the possibility of unnecessary reformulation or market disruption. A generic screen would not answer the question. The client needed a method that addressed the exposure pathway clearly enough to support a technical response specific to the matter.1
The method shift
After reviewing the technical problem, ARE Labs reframed the test around a narrower question: how much TiO2 was present in the aerosolized fraction small enough to be relevant to inhalation under the matter's criteria? This shifted the focus from broad material screening to the inhalation-relevant dose.1
The revised protocol combined controlled aerosolization, NGI cascade separation, gravimetric mass collection, and third-party elemental TiO2 analysis when sufficient respirable mass was available. ARE Labs also worked through the technical review process with the test laboratory involved in the matter, allowing the revised protocol to be used for retesting.1
Why cascade impaction fit the question
The choice of a cascade impactor was grounded in inhalation aerosol science. FDA guidance for inhalation products identifies aerodynamic particle size distribution as a key performance attribute and notes that APSD is typically measured with an appropriate cascade impactor. ARE Labs applied that measurement principle to the cosmetic powder exposure question without treating the cosmetic as a drug product.1,5
This distinction kept the method appropriately narrow. The study did not assume that a pressed cosmetic powder should be evaluated as an inhaled medicine. Instead, it recognized that when the risk question concerns airborne respirable particles, aerosol science provides a more relevant way to isolate the fraction being compared.1,3,5
- Representative powder samples were aerosolized under controlled laboratory conditions.1
- The aerosol passed through an NGI cascade impactor so collected mass could be separated by aerodynamic size.1
- The <10 um fraction was weighed and analyzed for TiO2 when enough material was collected.1
- When collected respirable mass was too low for elemental quantification, the comparison used a conservative 100% TiO2 upper-bound assumption.1
The accepted method focused on the fraction below 10 micrometers rather than treating all bulk product material as equally relevant. When sufficient respirable material was collected, that fraction could be submitted for elemental TiO2 analysis. When the collected mass was too low, the comparison used a conservative upper-bound assumption that treated all collected respirable mass as TiO2.1,3
What the data showed
All four anonymized product variants remained below the case-specific fail threshold. Products A and B passed using the 100% TiO2 upper-bound assumption. Products C and D had measured TiO2 concentrations of 4.57% and 1.09%, respectively, in the collected respirable fraction.1
Source: anonymized ARE Labs respirable TiO2 method report.
- Product names and matter identifiers are intentionally excluded.
- Products A and B use a conservative upper-bound assumption for the TiO2 mass comparison.
| Product | Powder aerosolized | <10 um mass collected | TiO2 in <10 um fraction | TiO2 mass compared | Fail threshold | Result | % of threshold |
|---|---|---|---|---|---|---|---|
| Product A | 21.60 g | 13.6 mg | 100.00% upper-bound assumption | 13.6 mg | 240.87 mg | Pass | 5.65% |
| Product B | 25.17 g | 4.3 mg | 100.00% upper-bound assumption | 4.3 mg | 280.70 mg | Pass | 1.53% |
| Product C | 4.62 g | 159.4 mg | 4.57% | 7.28 mg | 51.48 mg | Pass | 14.14% |
| Product D | 4.15 g | 215.8 mg | 1.09% | 2.35 mg | 46.33 mg | Pass | 5.07% |
Products A-D are anonymized. A 100% upper-bound assumption means the collected <10 um mass was conservatively treated as entirely TiO2 because collected mass was too low for third-party elemental quantification.
The conservative treatment of Products A and B avoided implying greater precision than the collected respirable mass could support. The mass was too low for elemental quantification, so the analysis treated the entire collected respirable fraction as TiO2. Both products still remained below the case-specific threshold. Products C and D yielded measured TiO2 concentrations in the collected respirable fraction, and those values also remained below the comparison threshold.1
What the client could use
The client received a data package tied to the inhalation-relevant fraction rather than a broad composition screen. This separated the presence of titanium dioxide in the cosmetic powder from the amount of TiO2 found in the respirable aerosol fraction generated under the test method.1,3
The documented technical outcome was clear: all four tested product variants passed the matter's case-specific criteria, and the matter was dismissed. The result does not make this method a universal Prop 65 answer for every powder product. It did, however, provide this client with an evidence package aligned with the specific dispute.1
The same principle applies to future cosmetic powder evaluations: define the exposure pathway, isolate the relevant particle-size fraction, document the aerosol generation conditions, and align the comparison with the current regulatory context and any criteria specific to the matter.1,4
This case offers a practical lesson for cosmetic and personal-care manufacturers. A scientifically defensible assessment should determine whether TiO2 is present in an airborne, unbound, respirable form; whether the method isolates that fraction before TiO2 is quantified; whether aerosol generation is controlled and reproducible; and whether the resulting data package is sufficient for legal, regulatory, quality, and product-safety review.1,2,3
Summary
The client needed evidence that addressed the specific respirable TiO2 question, not merely a broad screen for titanium dioxide in a powder compact. ARE Labs supported the matter by developing a respirable-fraction method, coordinating the test approach, and generating a documented data package. The interpretation remained tied to the anonymized results: all four product variants passed the matter's criteria.1