Lyral

Lyral is a trade name of hydroxymethylpentylcyclohexenecarboxaldehyde (HMPCC), a synthetic fragrance. Other trade names for it are Kovanol, Mugonal and Landolal.

Chemistry

The IUPAC name of the compound is 4-(4-hydroxy-4-methylpentyl)cyclohex-3-ene-1-carbaldehyde. The EU entry for HICC names the 3- and 4-(4-hydroxy-4-methylpentyl)cyclohex-3-ene-1-carbaldehyde, with CAS numbers 51414-25-6 and 31906-04-4. The molecule has the formula C₁₃H₂₂O₂ and a molar mass of about 210.3 g/mol. It is a liquid with a density of 0.995 g/mL at 20 °C. Its EC number is 250-863-4, and its INCI name is Hydroxyisohexyl 3-Cyclohexene Carboxaldehyde.

Allergen status and regulation

Lyral is known to act as a skin allergen and is listed as such in EU Directive 76/768/EEC. Before the ban, entry 79 of Annex III to Regulation (EC) No 1223/2009 required HICC to be named in the list of ingredients when its concentration exceeded 0.001 % in leave-on products and 0.01 % in rinse-off products.

The Scientific Committee on Consumer Safety (SCCS) concluded in its opinion of 26-27 June 2012 that HICC, atranol and chloroatranol should not be used in cosmetic products, as they are the fragrance allergens which caused the highest number of contact allergy cases in past years. Since the 1999 opinion on fragrance allergy, HICC has been the most frequently reported chemical causing fragrance allergy. The SCCS considered the number of HICC allergy cases documented over the last decade exceptionally high and judged continued exposure to HICC unsafe even at concentrations as low as 200 ppm.

An earlier opinion, from the SCCP in 2003, concluded that 200 ppm of HICC would be tolerated by the majority of sensitised individuals and would have a low potential to induce sensitisation. Voluntary recommendations to lower use concentrations of HICC to the 2003 level are not reflected in the available evidence and were judged insufficient.

Commission Regulation (EU) 2017/1410 of 2 August 2017 added HICC to Annex II of Regulation (EC) No 1223/2009, the list of substances prohibited in cosmetic products. From 23 August 2019 cosmetic products containing HICC could not be placed on the Union market, and from 23 August 2021 they could not be made available on it. The restriction in entry 79 stayed in force until products containing HICC could no longer be made available, so the deletion of that entry was deferred. Manifestations of contact allergy to fragrances are normally confined to the skin, and consumers with such an allergy are often aware that they cannot tolerate scented products.

Patch testing

HICC is patch-tested independently at 5 % in petrolatum, or as part of fragrance mix II, within the European baseline series of patch tests. HICC was part of the Spanish baseline series from 2012 until 2022, when it moved to the Spanish extended series. In Spain, 96 (0.8 %) of 12,029 patients tested between June 2018 and December 2023 were positive to HICC. The most recent European studies indicate a decrease in the prevalence of sensitization to HICC in recent years, currently around 1 %. In the European Surveillance System on Contact Allergies, sensitization to HICC fell from 1.7 % in 2009 to 1.3 % in 2020.

Fragrance mix II is a 14 % petrolatum mixture of six fragrances: hexyl cinnamic aldehyde at 5 %, HICC, coumarin and farnesol at 2.5 % each, citral at 1 % and citronellol at 0.5 %. HICC is the most important ingredient of the mix, which is why it is also tested on its own. In the Spanish series, 396 (3.3 %) of the 12,029 patients were positive to fragrance mix II. In most studies, about 15-20 % of HICC-positive patients would be missed if only fragrance mix II were tested, and for this reason some authors have recommended removing HICC from the baseline series.