The client challenge
A prestige cosmetics brand was facing a California Proposition 65 matter involving titanium dioxide in pressed cosmetic powder products. The practical dispute was not only whether TiO2 was present; it was whether the testing approach matched the inhalation exposure question. A bulk-material screen could identify 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, and the current public fact sheet notes that the form on the Proposition 65 list is limited to airborne particles measuring 10 micrometers or less. That distinction made particle-size separation central to the test design.2,3,4
For the client, the stakes included product risk, legal exposure, reputational pressure, and the possibility of unnecessary reformulation or market disruption. The client needed more than a generic screen. They needed a method that asked the exposure-pathway question clearly enough to support a matter-specific technical response.1
The method shift
ARE Labs reviewed the technical problem and reframed the test around a narrower question: how much TiO2 was present in the aerosolized fraction small enough to be inhalation-relevant under the matter's criteria? That shifted the matter from a broad material-screening question to an inhalation-relevant dose question.1
The revised protocol used controlled aerosolization, NGI cascade separation, gravimetric mass collection, and third-party elemental TiO2 analysis when enough respirable mass was available. ARE Labs also worked through the technical review process with the test laboratory involved in the matter so the revised protocol could be used for retesting.1
Why cascade impaction fit the question
The cascade impactor choice came from inhalation aerosol science. FDA inhalation-product guidance describes aerodynamic particle size distribution as a key performance attribute and notes that APSD is typically tested 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
That distinction kept the method appropriately narrow. The point was not to claim that a pressed cosmetic powder should be evaluated as an inhaled medicine. The point was that, when the risk question involves airborne respirable particles, aerosol science gives a more relevant way to isolate the fraction that should be 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 enough respirable material was collected, the fraction could be sent for elemental TiO2 analysis. When collected mass was too low, the comparison used a conservative upper-bound assumption that treated the collected respirable mass as entirely TiO2.1,3
What the data showed
The four anonymized product variants all stayed below the case-specific fail threshold. Products A and B passed under the 100% TiO2 upper-bound assumption, while Products C and D had measured TiO2 concentrations of 4.57% and 1.09% 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 was important because it avoided overstating precision where collected respirable mass was too low for elemental quantification. Even when the full collected respirable mass was treated as TiO2, both products remained below the case-specific threshold. Products C and D provided measured TiO2 concentrations in the collected respirable fraction, and those measured 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. That helped separate the presence of titanium dioxide in a cosmetic powder from the amount of TiO2 in the respirable aerosol fraction generated by 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. That outcome did not turn the method into a universal Prop 65 answer for every powder product, but it gave this client a stronger evidence package for the actual dispute.1
For future cosmetic powder questions, the same principle still matters: define the exposure pathway, isolate the relevant size fraction, document the aerosol generation conditions, and align the comparison with current regulatory context and any matter-specific criteria.1,4
Cosmetic and personal-care manufacturers can take a practical lesson from the case. A scientifically defensible assessment should ask whether TiO2 is present in an airborne, unbound, respirable form; whether the test method isolates that fraction before quantifying TiO2; whether aerosol generation is controlled and reproducible; and whether the resulting data package is strong enough for legal, regulatory, quality, and product-safety review.1,2,3
Summary
In summary, the client needed evidence that matched the specific respirable TiO2 question, not just 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, generating a documented data package, and keeping the interpretation tied to the anonymized results that all four product variants passed.1