The final SCCS Opinion on the safety of Thiomersal and Phenylmercuric salts as preservatives in cosmetic products was published on 10 February 2026, in its final version dated 2 February 2026 and identified as SCCS/1686/25. The document focuses on their use as preservatives in eye cosmetic products, which is the area in which these mercurial compounds are still considered under European cosmetic legislation.
The Committee’s conclusion is clear: the use of Thiomersal and Phenylmercuric salts is not considered safe at the concentration levels currently permitted in cosmetic products, because the margin of safety (MoS) calculated on the basis of renal toxicity as the most sensitive endpoint is below 100, and uncertainties regarding genotoxicity also remain. The SCCS further states that the potential risk to human health is aggravated by additional exposure to mercurial compounds from sources other than cosmetics.
Which substances are actually assessed in the SCCS Opinion
The assessment refers to Thiomersal and to Phenylmercuric salts used as preservatives. The document notes that, while Thiomersal is a specific substance, the term Phenylmercuric salts covers various salts of the phenylmercury cation, such as acetate, benzoate, borate, bromide or chloride. However, for the detailed toxicological assessment, the SCCS works mainly with Thiomersal and phenylmercuric acetate, because those were the substances for which the most relevant data were available.
This distinction matters quite a lot, because in cosmetic regulation it is not enough to look at the generic name of a family of substances. It is necessary to understand exactly which data support the assessment and to what extent that evidence does, or does not, cover all the variants included within the same category.
Current regulatory status of Thiomersal and Phenylmercuric Salts
The Opinion recalls that Regulation (EC) No 1223/2009 currently permits the use of Thiomersal and Phenylmercuric salts (including borate) only in eye cosmetic products, at a maximum concentration of 0.007% expressed as mercury, whether used separately or in combination. In addition, products containing these substances must include the warnings “Contains Thiomersal” or “Contains Phenylmercuric compounds” on the label.
In other words, these are not widely used preservatives within current cosmetics, but rather highly restricted compounds already subject to specific conditions. Precisely for that reason, a negative final SCCS opinion becomes particularly relevant: when a substance was already under close scrutiny and still fails the current assessment, the subsequent regulatory pressure is usually fairly predictable.
Why the SCCS considers them unsafe
The core of the scientific conclusion lies in two elements. The first is the margin of safety, which the SCCS calculates using renal toxicity as the most sensitive effect. In the case assessed, the Committee states that this margin of safety falls below 100, which is the conventional reference threshold in this type of evaluation. The second element is that the available evidence on genotoxicity remains unresolved, so there is no sufficient basis to dismiss that concern.
More specifically, the document states in its discussion that neither Thiomersal nor Phenylmercuric salts can be considered safe at the use concentration of 0.007% as Hg in eye cosmetic products. It further concludes that combined exposure from other sources of mercury increases the safety concern even more. In other words, it is not that the SCCS sees a comfortable margin with an extra warning attached. The conclusion is directly negative under the currently permitted conditions.
Aggregate exposure: a key factor in the assessment
One of the most relevant aspects of this Opinion is that the SCCS does not look at the cosmetic product in isolation. The text underlines that the potential risk is aggravated by additional exposure to mercurial compounds from sources other than cosmetics. This fits with an increasingly clear regulatory trend: the safety of a substance is not assessed only on the basis of its presence in one individual product, but also on the basis of the potential sum of exposures.
For manufacturers and brands, this approach has an important implication. Even when cosmetic use appears residual or limited to a specific category, the safety case may weaken if the substance forms part of a problematic toxicological profile in the context of overall exposure. And with mercury in particular, the room for pretending nothing is happening is rather limited.
What may happen next at regulatory level
The SCCS Opinion does not in itself amend the Cosmetic Regulation, but it does provide the scientific basis for the European Commission to adopt subsequent regulatory measures. When a final opinion concludes that a substance cannot be considered safe under the currently authorised conditions, the most likely scenario is usually a revision of the annexes of Regulation 1223/2009, either to further restrict the use or to remove the current authorisation. This is a reasonable regulatory inference based on the role SCCS opinions play within the European cosmetic safety system.
Therefore, although the concrete legal change will still depend on a later decision by the Commission, the scientific conclusion already points in a very clear direction. And usually, when the SCCS leaves so little interpretive space, it is not because it is inviting the industry to relax.
What cosmetic companies should already be reviewing
For companies that still work with Thiomersal or Phenylmercuric salts in eye products, this Opinion should trigger an immediate review of several points:
- current formulation and actual concentration expressed as mercury;
- product technical documentation, including the PIF and the CPSR;
- the safety justification currently being used;
- applicable labelling and warnings;
- availability of alternative preservatives;
- and transition strategy in the event of a possible upcoming regulatory change.
Although the scientific opinion does not yet amount to an immediate prohibition, waiting until the legal amendment is published before starting to analyse the impact is usually a fairly expensive business habit. Even more so when dealing with mercurial substances, where regulatory and reputational tolerance tends to be, let us say, limited.
How SHAPYPRO can help
In this context, SHAPYPRO can help manufacturers and brands review the impact of the final SCCS Opinion on Thiomersal and Phenylmercuric salts, assessing whether there are immediate regulatory risks for their eye products and reviewing the associated technical documentation. This includes the review of formulations, alternative preservatives, PIF, CPSR, labelling and adaptation strategy in the event of a possible amendment to the European Cosmetic Regulation. This type of prior technical review is usually much more comfortable than improvising once the legal update is already on the table.
Conclusion
The final SCCS Opinion on Thiomersal and Phenylmercuric salts leads to a firm conclusion: these preservatives are not considered safe at the levels currently permitted for eye cosmetic products, due to an insufficient margin of safety, uncertainties regarding genotoxicity, and the context of additional exposure to mercurial compounds from other sources.
For the cosmetic industry, this should not be seen as just another scientific note to file away without emotion. It is a serious regulatory signal pointing towards a possible regulatory revision and requiring a review of products, documentation and compliance strategy. Because when mercury enters the regulatory conversation, the prudent part of the matter stops being optional rather quickly.