Caprylhydroxamic Acid: A Growing Allergen in Skincare Products

Abstract

A 70-year-old woman presented with bilateral upper and lower eyelid eczema and cheilitis persisting for 1 year despite dermocorticoids (Figure 1A).

Initial patch testing with European baseline series revealed contact allergy to methylchloroisothiazolinone and methylisothiazolinone (MCI/MI). However, the eczema persisted and spread despite MCI/MI avoidance.

A second-round of patch testing with the European baseline series, cosmetic series (Chemotechnique Diagnostics, Vellinge, Sweden) and 11 personal care products was carried out and found out to be positive 2+ on day 3 for the semi-open test with her cleaning lotion, universal lotion NOREVA (NOREVA laboratory, France), despite the absence of MCI/MI. Thus, patch testing was performed with lotion's ingredients provided by the firm and revealed strong contact allergy 3+ for a component named SPECTRA STAT E, a commercial blend containing caprylhydroxamic acid (CHA), methylpropanediol (MP), and ethylhexylglycerin (EE). As the latter had previously tested negative, CHA and MP were suspected allergens.

Further patch testing was conducted using SPECTRA STAT E (CHA, MP and EE) and SPECTRA STAT (CHA alone) with three different concentrations in petrolatum (1%, 2% and 5% pet). All formulations tested positive for 1+ or 2+ at lower concentrations, and 3+ at higher concentrations on D3 (Figure 1B), confirming CHA as the responsible allergen. The results of the key patch tests are detailed in Table 1. The contact allergy to the universal lotion NOREVA is, therefore, linked to caprylhydroxamic acid, although the responsibility of methylpropanediol cannot be ruled out as it is not available from the firm on its own.

Contact allergies to cosmetics are very common, with a wide variety of clinical presentations [1] and often leading to patch testing. The majority of these cases are caused by fragrances and preservatives [2].

Spectrastat E is a preservative system developed by INOLEX that contains caprylhydroxamic acid, a natural chelating agent inhibiting yeast and mould growth; ethylhexylglycerin, a skin-conditioning agent preventing bacterial proliferation; and methylpropanediol, a formulation carrier. This is, therefore, used in emulsions, creams, lotions and surfactant-based products such as shower gels, facial cleansers and shampoos.

In the published literature, there has been only one documented contact allergy being attributed to CHA related to Apobase moisturisers. This occurrence coincided with a modification in the formulation of cosmetic products, which included the preservative Phenostat between the years 2014 and 2016. This mixture contains phenoxyethanol, caprylhydroxamic acid and methylpropanediol [3]. The study, which was conducted on 39 patients in Finland, showed positive reactions to the novel Apobase formulas and to caprylhydroxamic acid. However, no positive reactions were observed to the old formulas or to the other components of Phenostat, thus confirming caprylhydroxamic acid as an emerging contact allergen. Following this contact allergy epidemic, Phenostat had been withdrawn from Apobase in 2016 in Finland. They also performed patch tests with different concentrations on patients and on healthy controls, determining that the ideal patch testing dilution for CHA for patch tests is 1%.

Whereas MP is used as a solvent and is not described in the literature as a potential allergen.

Our case is the first described since the removal of CHA from Apobase in 2016.

Caprylhydroxamic acid (INCI name: CAPRYLHYDROXAMIC ACID) seems to be an emerging allergen responsible for severe contact allergy. It is likely that it will be used more and more in cosmetics because it is considered to be derived from natural products.

It is currently used in skin and body creams, hair products, makeup, sunscreens, antiperspirants and deodorants and in a variety of cleaning products and facial cleansing gels, as in our case.

The patch tests conducted were positive for MI, MCI/MI and CHA. This could be the result of a coincidental discovery or the sign of a potential cross-reaction, necessitating further analysis with a larger sample size, even though the molecules in question do not share a similar chemical structure.

Moreover, this report highlights the need for testing patient-used cosmetics alongside commercial patch series when investigating contact allergies, especially in reformulated products.

Valentine Theret: conceptualization, investigation, writing – original draft, writing – review and editing. Estelle Burle: writing – original draft, writing – review and editing, supervision. Françoise Giordano: conceptualization, supervision, writing – original draft, writing – review and editing.

The patient in this manuscript has given written informed consent to publication of their case details and photographs.

The authors declare no conflicts of interest.