The Risk Assessment Committee (RAC) of the European Chemicals Agency (ECHA) has recently published two scientific opinions that may significantly affect manufacturers and importers of fragrance substances, including natural essential oils. The opinions propose that two groups of commonly used fragrance substances be classified as category 1B reproductive toxicants, which could trigger far-reaching consequences for CLP classification, safety data sheets (SDS), and product labelling.

New RAC Opinions and CLP Classification – What Do the Proposals Cover?

The new opinions focus on two groups of fragrance substances: one related to bourgeonal, the other to cyclamal. In both cases, the basis for the proposed CLP update is the assumption that these substances are metabolised into structurally similar compounds that may negatively affect reproductive function.

Bourgeonal Group – Metabolism to TBBA and Reproductive Toxicity Concerns

This group was defined based on two key substances:

• Lysmeral [CAS 80-54-6] – 2-(4-tert-butylbenzyl)propionaldehyde

• 4-tert-butylbenzoic acid (TBBA) [CAS 98-73-7] – a metabolite of lysmeral

Both substances already have a harmonised CLP classification as reprotoxic category 1B. According to RAC, four other structurally similar substances within the group are also metabolised into TBBA, and therefore may exhibit the same toxicological profile:

• 3-(4-tert-butylphenyl)propionaldehyde [CAS 18127-01-0]

• 4-tert-butyltoluene [CAS 98-51-1]

• 4-tert-butylbenzaldehyde [CAS 939-97-9]

• Methyl 4-tert-butylbenzoate [CAS 26537-19-9]

RAC’s assessment highlighted the formation of TBBA–CoA adducts, where TBBA binds to coenzyme A (CoA), a molecule essential in lipid biosynthesis, including in reproductive tissues. The committee concluded that the mechanism observed in animal studies could not be ruled out in humans.

Cyclamal Group – Structural Similarity and Potential Toxic Effects

The second group of substances under evaluation includes compounds that are either known or expected to be metabolised into 4-isopropylbenzoic acid [CAS 536-66-3], a compound structurally similar to TBBA. These include:

• 3-p-cumenyl-2-methylpropionaldehyde [CAS 103-95-7]

• 3-p-cumenylpropionaldehyde [CAS 7775-00-0]

• 4-isopropylbenzaldehyde [CAS 122-03-2]

• 4-isopropylbenzoic acid [CAS 536-66-3] (not yet classified under CLP)

This group’s classification was based on toxicological data related to p-cymene [CAS 99-87-6], a compound found naturally in various essential oils, including tea tree oil.

Essential Oils and CLP Classification – The Case of Tea Tree Oil

In November 2023, RAC issued an opinion that tea tree oil should be classified as category 1B reproductive toxicant, also based on its potential metabolism into a compound that could bind to CoA. Although this proposal was initially suggested for inclusion in the 23rd ATP to CLP, it was ultimately excluded from the version of the draft regulation notified to the WTO in September 2024.

The case remains a key example of how essential oils, often considered “natural” and therefore safe, are increasingly being scrutinised under the lens of modern toxicological assessment and CLP regulation.

Safety Data Sheet (SDS) Updates and Supplier Obligations

If the proposed classifications by RAC are adopted, they will lead to mandatory updates to safety data sheets (SDS), product labelling, and classification in accordance with CLP Regulation (EC No 1272/2008). This will directly affect:

• manufacturers and importers of fragrance substances and essential oils,

• companies in the cosmetics, perfumery, and household chemicals sectors,

• producers of specialty chemicals such as cleaning agents, candles, and air fresheners.

The CLP update will likely also require companies to submit revised notifications to ECHA databases (e.g., IUCLID, PCN), and reassess exposure scenarios and hazard communication measures.

Conclusion: What Does the New CLP Classification Mean for the Industry?

These new RAC opinions illustrate an increasing trend toward grouping and classifying substances based on metabolic pathways and structural similarity, even when direct human data is limited. While the industry continues to argue that the reproductive effects observed in animal studies may not apply to humans, ECHA follows the precautionary principle, especially when mechanistic data suggest a credible risk.

Stakeholders using or formulating products with fragrance ingredients or essential oils should closely monitor legislative developments and prepare in advance for a potential CLP classification update and the necessary SDS revisions.