Scientific Update on 4-MBC, Formaldehyde-Releasing Preservatives and Homosalate in Cosmetics: New Opinions from the UK SAG-CS

Between April and May 2025, the Scientific Advisory Group on Chemical Safety of Non-Food and Non-Medicinal Consumer Products (SAG-CS), the expert body advising the UK Office for Product Safety and Standards (OPSS), issued three separate opinions reassessing the safety of (i) formaldehyde-releasing preservatives, (ii) the UV filter homosalate, and (iii) the UV filter 4-methylbenzylidene camphor (4-MBC). The conclusions point to imminent regulatory changes under the amended UK Cosmetic Products Regulation (UK CPR 1223/2009) and will require reformulation of numerous cosmetic products.

Table of contents

1. Regulatory Context and Methodological Scope

2. Formaldehyde-Releasing Preservatives: From 0.05 % to 10 ppm

3. Homosalate: Safe up to 10 % Under Conditions

4. 4-MBC: No Safe Level Established

5. Conclusion

   
   

SCCS on 4-MBC, formaldehyde and homosalate releasers in cosmetics

1. Regulatory Context and Methodological Scope

Following the UK’s departure from the EU, Regulation (UK) No 1223/2009 on cosmetic products remains in force, but its technical interpretation now rests with the SAG-CS. The new opinions are based on:

• Systematic reviews of published toxicological data and industry dossiers.

• Risk assessments built on margin-of-safety (MoS) calculations and derived systemic exposure doses (SED).

• Application of the precautionary principle whenever the data are insufficient to ensure consumer safety.

  
  

2. Formaldehyde-Releasing Preservatives: From 0.05 % to 10 ppm

Current Status

Free formaldehyde is banned outright (Annex II, entry 1577), yet several Annex V preservatives can release it in situ. Whenever free formaldehyde exceeds 0.05 % (500 ppm), the label must state “contains formaldehyde”.

Key SAG-CS Findings

Aspect	Detail
Clinical evidence	Allergic reactions reported below 0.05 %.
Toxicological conclusion	The 0.05 % threshold does not protect sensitised individuals.
Recommendation	Lower the labelling trigger to 10 ppm (0.001 %) for both leave-on and rinse-off products.

The group considers current analytical methods robust enough to monitor these levels and believes the measure will address cumulative daily exposure

3. Homosalate: Safe up to 10 % Under Conditions

Regulatory Framework

Homosalate is listed in Annex VI (entry 3) as a UV filter permitted up to 10 %.

Opinion Highlights

• Exposure data: Real-world concentrations ≤ 10 % in sunscreens yield SPF 10–50.

• Endocrine-disruption evidence: In vitro assays show oestrogenic/anti-androgenic activity, but in vivo relevance is limited.

• Risk assessment: MoS > 100 using a NOAEL of 100 mg kg-¹ bw day-¹; no significant adverse effects in repeated-dose studies.

Conclusion: Homosalate is safe up to 10 % in all dermal applications evaluated, provided purity specifications are met and nanoparticle exposure is controlled

4. 4-MBC: No Safe Level Established

4-MBC (currently allowed up to 4 % under Annex VI, entry 19) is under review for potential thyroid- and oestrogen-disrupting effects.

• Data gaps: Absence of updated genotoxicity and reproductive-toxicity studies.

• Current SED: ≈ 4-fold higher than in previous assessments, drastically lowering the MoS.

• Outcome: Available evidence does not allow derivation of a safe concentration. Industry is requested to submit a full toxicological package; otherwise, restrictions or withdrawal are anticipated

  
  

5. Implications for Manufacturers and Responsible Persons

Ingredient Group	Recommended Actions
Formaldehyde releasers	• Reformulate or justify ≤ 10 ppm free formaldehyde. • Implement residual-formaldehyde testing on finished batches. • Update labels in anticipation of Annex V changes.
Homosalate	• Verify purity and absence of endocrine-active contaminants.
4-MBC	• Consider alternative UV filters (e.g., octisalate, octocrylene). • Suspend development of new products with 4-MBC until a definitive opinion is published.

Conclusion

SAG-CS Opinions 16, 17 and 18 reinforce the UK’s move toward a continuously updated, risk-based regulatory model. The drastic reduction of the free-formaldehyde threshold and the uncertainty surrounding 4-MBC foreshadow significant reformulation demands, whereas retention of homosalate at 10 % highlights the UK regulator’s flexibility compared with the EU’s more conservative stance. Companies will need to adapt compliance strategies and strengthen post-marketing surveillance to safeguard consumer safety and commercial viability in the dynamic post-Brexit landscape.