Understanding Chemical Risk Assessment: Exposure and Product Safety
- Jun 11
- 5 min read
Updated: Jun 16
A product may contain a hazardous substance without necessarily presenting an unacceptable risk, provided that user exposure remains controlled. Conversely, an apparently low concentration is not always sufficient to guarantee safety. Everything depends on the substance’s toxicity, the way it is released, and the actual conditions of use.
Chemical risk assessment therefore seeks to answer two complementary questions: what are the hazardous properties of the substances present, and how, and to what extent, can the user be exposed to them?
A two-pillar approach
Identifying the hazards of chemical substances present in a product
Hazard assessment aims to identify the potential adverse effects of substances present in an article, mixture, or chemical product. It relies on all available information, including harmonized classifications or self-classifications under the CLP Regulation, Safety Data Sheets (SDS), experimental toxicological data, scientific literature, opinions issued by health agencies, and information from regulatory dossiers.
Where sufficient data are available, this step leads to the selection or development of an appropriate toxicological reference value. This may be a Reference Dose (RfD), a Reference Concentration (RfC), or, where such values are unavailable, a toxicological point of departure such as a NOAEL/NOAEC (No Observed Adverse Effect Level/Concentration) or a LOAEL/LOAEC (Lowest Observed Adverse Effect Level/Concentration), to which uncertainty factors are applied.
The selected reference value must always be consistent with the exposure route, exposure duration, and target population.
For threshold effects, this reference corresponds to an exposure level below which no adverse health effects are expected under the assessed conditions. For non-threshold effects (such as carcinogenicity) or when available data are insufficient, the assessment must adopt a more precautionary approach and clearly document uncertainties.
Estimating real-World user exposure to chemical substances
Exposure assessment aims to determine the conditions under which users are actually exposed. It must cover both normal conditions of use and reasonably foreseeable conditions of use.
Accidents, intentional misuse, or clearly unforeseeable behaviours require separate prevention, information, or risk management measures and should not be confused with the use scenario selected for concluding on product safety.
The precautions provided on product labels or instructions for use are therefore directly linked to the assumptions used in the assessment. If users deviate from these conditions, product safety can no longer be guaranteed.
Characterising chemical risk
Risk characterisation consists of comparing estimated exposure with an appropriate toxicological reference value. Depending on the context, this comparison may take the form of a Risk Characterisation Ratio (RCR) or a Margin of Exposure (MOE).
Risk does not depend solely on the presence of a hazardous substance. It also depends on substance concentration, the route of exposure, and the conditions under which the substance is released, inhaled, ingested, or handled. It is this combination of hazard and exposure that allows conclusions to be drawn regarding whether the risk is adequately controlled.
Fragrance Diffusers: a practical example of chemical risk assessment
A fragrance diffuser is a good example of a consumer product for which a pleasant fragrance can sometimes obscure the underlying chemical reality of the product.
Whether it is a reed diffuser, nebuliser, electric diffuser, or liquid refill system, safety must be demonstrated based on the substances present, their mode of release, and the anticipated exposure of users.
Verifying the applicable regulatory framework
For companies formulating, importing, or marketing fragrance diffusers within the European Union, several regulatory checks are required:
Verify the classification of the mixture and its substances under the CLP Regulation and ensure that labelling and packaging are consistent with this classification.
Consider any applicable supplemental hazard statements, including those related to sensitising substances when regulatory thresholds are exceeded.
Ensure that substances are registered under REACH where required, or covered by supply chain information when the company acts as a downstream user.
Confirm that the intended use (“air freshener”, “air care product”, or “indoor air diffusion”) is covered by identified uses (Product Category PC3), Safety Data Sheets, and, where relevant, exposure scenarios provided by suppliers.
Check restrictions applicable to substances contained in the mixture, including those listed under REACH Annex XVII, as well as any obligations relating to Substances of Very High Concern (SVHCs) or substances subject to authorisation.
Maintain Safety Data Sheets and supplier information and make them available where required by regulation.
Verify Poison Centre Notification obligations and UFI assignment requirements when the mixture is classified for physical or health hazards and intended for consumer or professional use.
Determine whether product-specific regulatory obligations apply.
These checks form the foundation of risk assessment. They help ensure composition control, data traceability, and accurate communication to users, while also determining whether an additional assessment is required to demonstrate compliance with the General Product Safety Regulation (GPSR). (See the GPSR blog post).
Selecting appropriate toxicological reference values
For fragrance diffusers, inhalation is generally the primary exposure route. Dermal exposure should also be considered when users handle refills, fill reservoirs, clean devices, or otherwise come into contact with the fragrance solution.
For each relevant substance, it is therefore necessary to identify a toxicological reference value appropriate to the exposure route and expected duration of use, whether acute, repeated, or chronic. Where available data are limited, assessors must justify their choices, document uncertainties, and, where appropriate, adopt a conservative approach.
Building a realistic exposure scenario for a fragrance product
For fragrance diffusers, exposure is highly dependent on use conditions. Parameters that should be documented include:
Type of diffuser (reed diffuser, electric plug-in diffuser, nebuliser, automatic spray system, refill, etc.)
Quantity of product released and emission rate
Concentration of substances within the mixture and their physicochemical properties, particularly volatility
Emission duration, user presence time within the room, and frequency of use
Room volume, air exchange rate, and ventilation conditions
Potential handling activities such as installation, refilling, replacement of refills, and cleaning
Potentially exposed populations, particularly children, pregnant women, and individuals with asthma or allergies, where relevant to the intended use
A modelling tool such as ConsExpo, or an equivalent consumer exposure model, can be used to estimate exposure based on these parameters.
The assumptions used should be realistic, sufficiently protective, and consistent with the instructions and precautions provided to consumers.
Interpreting the results of a chemical risk assessment
Where estimated exposure remains below the selected toxicological reference value, the risk may be considered adequately controlled under the assessed conditions.
However, if exposure approaches or exceeds the selected reference value, or if available data do not allow a sufficiently robust conclusion, the formulation, mode of diffusion, or conditions of use should be reconsidered.
From risk assessment to risk management: ormulation, Use Conditions, and Instructions for Use
The objective of chemical risk assessment is not simply to produce a technical dossier. It should support practical decisions regarding product formulation, design, and consumer information.
Several risk management measures may be implemented, including reducing the concentration of a substance, substituting an ingredient, modifying the emission rate, limiting recommended duration of use, discouraging use in specific rooms or situations, improving ventilation recommendations, strengthening labelling, or redesigning the device itself.
Conclusion : demonstrating the chemical safety of the finished product
A fragrance diffuser intended solely to provide fragrance remains a consumer chemical product. Its safety cannot be assumed based on a pleasant scent, an apparently low concentration, or the natural origin of its ingredients.
Safety assessment must rely on a structured approach: identifying hazards, selecting appropriate toxicological reference values, characterising actual user exposure, and comparing these values with anticipated exposure levels. This scientific and regulatory approach makes it possible to determine whether risk is adequately controlled under normal and reasonably foreseeable conditions of use.
Ultimately, regulatory compliance should not be viewed as a standalone administrative obligation, but rather as the extension of a fundamental objective: placing an enjoyable fragrance product on the market while demonstrating that it is safe for users under its intended conditions of use.
Author: Anna Chelle, Toxicologist and Chemical Risk Assessment & Safety service Manager
