Acrylates in artificial nails—Results of product analyses and glove penetration studies

Artificial nail materials are mixtures that are prone to contain several sensitizing (meth)acrylates. It is not known whether the listing of (meth)acrylates is correct in these products' packages. Protective gloves suited for nail work are needed.

2][3] Artificial nail materials, including gel nails, acrylic nails and gel lacquers are mainly based on methacrylates (esters of methacrylic acid).Gel nails and gel lacquers are viscous mixtures of reactive methacrylates that are hardened by UV light, whereas acrylic nails are prepared by mixing methacrylate monomer liquid with polymer powder.The most common allergen in nail professionals and users seems to be hydroxyethyl methacrylate, but allergy to other methacrylates and acrylates (esters of acrylic acid) exist, too.
The fact that nail materials belong under cosmetic regulation within the European Union (EU), may hamper their safe use: The package label must list all ingredients, but there is no requirement to state anything about their health hazards or personal protection nor are safety data sheets (SDSs) required. 4Also, products often contain a technical mixture of several acrylate compounds, and it is unknown whether the listings of ingredients are exhaustive.It is also uncertain whether protective gloves commonly used by nail professionals are an effective barrier against methacrylates and acrylates (later (meth)acrylates), many of which are known to break through disposable glove materials. 5,6 conducted an 'acrylate study' in 2019-2022 where we analysed our patient data on occupational allergic contact dermatitis 7 and asthma 8 due to acrylate compounds and looked specifically into exposure to (meth)acrylates in beauty salons and assembly sector. 9 The part of the study on beauty branch consisted of workplace observations and measurements in Helsinki area in South-Finland.We also collected nail products for chemical analysis and tested disposable protective gloves against acrylates.Here we present (1) our findings on the chemical analysis of (meth)acrylates in artificial nail materials and compare the results with package labelling, and (2) results on glove penetration analysis with two nail materials.

| Gel and acrylic nail product samples
Altogether 37 artificial nail material samples (31 gel nail products and 6 acrylic nail products; 20-100 μL of each) were collected in mini-centrifuge tubes from four nail salons between autumn 2019 and spring 2020.One salon sent their five samples to FIOH by mail.
The product samples are listed in Table 1.All samples were stored in a refrigerator upon arrival and diluted into 10% in acetone within 1-6 days.The solutions were later diluted to 100 μg/mL in acetone; 50 μL of internal standard (0.25 mg/mL cumene in acetone) was added to 1 mL of each solution, and these mixtures were analysed by gas chromatography-mass spectrometry (GC-MS)analysis.

| Glove penetration tests
We tested the penetration of two nail materials (a nail gel and an acryl nail liquid) through three disposable glove materials commonly used in nail salons (Table 2).We followed a previously reported method 10 with some modification.In short, we pipetted 50 μL of each nail product on a round piece of a disposable glove (diameter 8 cm) that was placed on top of a collecting filter (Whatman Glass Microfiber filter, diameter 25-47 mm).We then covered the glove pieces with a plastic film and a fibre-board plate (11 kg/m 2 ) for the selected test time that was either 5 or 20 min.After each test-time, the filters were immediately placed in 5 mL acetone and stored for GC-MS-analysis in a refrigerator.We ran separately three parallel samples for each glove material and test-time and report the mean of the total penetrated amounts.We analysed three parallel acetone extracts of the plastic film and of the collecting filter as such, similarly to other samples.

| Instrumental
Gas chromatography-mass spectrometry (GC-MS) analyses were performed with Agilent Technologies 6890N Series GC system with HP 5973 Mass Selective Detector (MSD).GC conditions: The capillary column was Agilent HP-5MS (30 m Â 0.25 mm Â 1 μm).Helium was T A B L E 1 Analysed gel nail and acrylic nail products, and (meth)acrylates in them according to GC-MS analysis and the package label.

| Identification
We identified (meth)acrylates using the reference substances and/or Wiley or NIST mass spectrum libraries.We could quantify those for which we had a reference substance.The limit of detection depended on the specific acrylate compound and was 0.40-4.34μg/mg sample.

| RESULTS
Table 1 presents the results of the analysis of nail materials.All except five samples contained one or more identifiable (meth)acrylates.The samples that did not contain (meth)acrylates were a shellac polish based on nitrocellulose and polymerized acrylates, two acryl nail powders based on polymerized acrylates, one gel primer and one topcoat.
In all other products, (meth)acrylates were stated in the labels and the products were also shown to contain them, but in all products, there was discrepancy between the listed (meth)acrylates and those discovered in the chemical analysis.The compounds most commonly found were HEMA (20/37 samples) and HPMA (9/37 samples); HEMA was mentioned in the ingredient list in 12 of the 20 that contained it and HPMA in 5 of the 9 products that contained it.For example, 5/6 of the 'Gel nail product line C' products were shown to contain HEMA and many contained also HPMA, but HEMA or HPMA was mentioned in none of the packages.The most often detected acrylate (ester of acrylic acid), IBA, was disclosed in one package label although identified in nine gel nail products.Product labels also listed (meth)acrylates that were not included in our method as reference substances nor identified by using spectrum libraries.

| DISCUSSION
We present as our main finding the analysis of allergens in a number of artificial nail materials.This study was conducted because we suspected that the ingredient lists of nail materials might not be comprehensive and indeed, we discovered several methacrylates and acrylates that were not disclosed in the packages.Almost all products were shown to contain at least one methacrylate or acrylate that was not disclosed.One product line, 'Gel nail product line C', is marketed as being 'clinically tested' and prepared 'avoiding excess allergens', but all except one of the products were shown to contain HEMA and many also HPMA, even though none of their packages disclosed them.This product line had SDSs that did not comply with the current standards, but that listed several methacrylates other than HEMA and HPMA and presented the previously used hazard statement 'R43-may cause sensitization by skin contact'.It is unethical to promote such products as 'natural' and even beneficial for nail health, as it may lead to a false feeling of security and thereby to lacking safety measures.Regardless of the discrepancy in the true composition and the ingredient list, we consider this product line as well as other products in the present analysis, quite typical nail materials which probably are not any safer than any other similar product lines on the market.
T A B L E 2 Results of the penetration tests with three disposable gloves and two nail products.BDDMA-peak was identified but could not be quantified due to its small amount.
The analysed nail products' ingredient lists included also (meth) acrylates for which we did not have reference substances.Some additional (meth)acrylates could be identified by spectrum libraries, but their quantification was not possible and there is some uncertainty in their identification as some (meth)acrylate compounds are structurally close to each other, and their spectra have thus resemblance.However, most of them, such as IBA, was identified with >90% certainty.
Covid 19-pandemic and changes in laboratory personnel during our study caused some problems in the analyses, and therefore (meth) acrylates eluating before 8 min in GC (e.g., EMA that was listed in the acrylic nail liquids) were not analysed.
We could not identify with certainty any (meth)acrylates in two gel nail products that were expected to contain them.The products might have been partly polymerized during delivery or sample preparation, or the result may be due to the limitations in our method.The nitrocellulose lacquer or the two acrylic nail powders were not expected to contain (meth)acrylates, but we still wanted to analyse them to make sure this was the case.
Our study showed that the health hazards of artificial nail materials and the allergens present in them are indeed difficult to identify based on their packages.One reason is the general lack of safety information, but also the false ingredient information that does not comply with the cosmetics legislation, plays a role.Based on our experience on nail salons during our study, many nail beauticians seem to be aware of the possibility of skin sensitisation to nail materials but are still uncertain about their own product lines because many of them are marketed as being safe. 9Also, some seem to think that if allergy is developed, changing to another product line will solve the problem.
The Scientific committee of consumer safety (SCCS) published an opinion in 2018 stating that HEMA and Di-HEMA Trimethylhexyl Dicarbamate 'are not likely to pose a risk of sensitisation, provided that their use is restricted to the nail plate only and contact with the adjacent skin is avoided' and that more analytical data are needed to exclude the possibility of other sensitisers in nail products. 11nce 2020, European cosmetics regulation has restricted HEMA and Di-HEMA Trimethylhexyl Dicarbamate to professional use only. 4These measures do not protect workers or nail consumers from allergies because (1) as shown here and in previous studies, 3 there are other contact sensitizers in nail products as they compose of mixtures of various (meth)acrylates, (2) we have shown that HEMA is present in many products without their label mentioning it, (3) also professionals have difficulties in avoiding skin contacts and understanding the sensitizing nature of the products they use and (4) it is quite easy for consumers to buy professional nail products either via the internet or from retailers that do not follow the legislation.
For clinicians, it is important to understand that all gel nail materials, gel lacquers and acrylic nail liquids contain various sensitizing methacrylates and probably also acrylates.Based on their chemical composition, gel nail materials are not safer than acrylic nail materials.
HEMA is an important screening allergen in nail beauticians, but also other contact allergens are present in the products.Based on the present findings, IBA that is known as an important allergen in glucose sensors, 12 could also be tested in nail beauticians and users of gel nails.Patients' own nail materials may well be tested, too.According to previous studies on related (meth)acrylates or their mixtures, 3 2% in petrolatum (possibly with a couple of downward dilutions) is considered as a suitable test preparation for a typical nail gel or acrylic nail liquid which often contain >50% (meth)acrylates.However, our analysis showed that, although not common, the amount of acrylates may exceed 10%, which means that nail products may need to be tested with more caution, for example in 1% petrolatum.
To promote skin protection, we performed a simplified penetration test to evaluate the suitability of three disposable glove materials which we had discovered to be used in nail salons for protection against nail (meth)acrylates.The test is easier and quicker than the standardized glove permeation test 13 and may also be used for reactive mixtures. 10Neither penetration nor permeation test methods can differentiate which process causes the movement of chemical through the material, 14 but the present method can be used for porous materials, and using weight may favour a chemical's penetration through small holes instead of its diffusion through intact materials.Neoprene proved to be the best material for the gel nail product, whereas none of the materials worked for the acrylic nail liquid as it penetrated or even degraded the materials quickly.The small amount of BDDMA penetration through 1/3 of neoprene gloves at 5 min was probably due to a small hole in the glove material at the test spot-this is always possible even in suitable glove materials.The tested nitrile rubber gloves were thinner than the neoprene gloves, which may partly explain their poorer performance compared to neoprene.Currently, EMA is common in acryl nail liquids, and it is also a powerful solvent.
Although not included in our method, EMA was the first ingredient listed in the package and it was the most likely ingredient to have caused the glove degradation and wrinkling.We conclude that disposable gloves should not be used at all when handling acrylic nail liquids and instead, workers should prevent skin contacts with especially careful work methods.
Professional nail technicians may have numerous contacts with nail materials daily, which is why they urgently need guidance about the risk of acrylate allergy and its prevention.Based on our observations at the worksites it seems very difficult to avoid skin contacts with nail materials entirely.Extreme care should be taken to perform the work so that no acrylates spread on the skin, or to surrounding surfaces and equipment which may subsequently act as sources of exposure.The regulatory authorities and cosmetic industry must start to communicate clearly and responsibly that gel and acryl nail materials may sensitize the skin.Acts towards better user guidance and more detailed package labelling requirements such as those currently applied to para-amino-derivative-containing hair dyes, could help to protect both professionals and consumers.
There are some limitations to this study.First, we only analysed compounds eluting after 8 min in the GC and could only include a limited number of reference substances; thus, we could not reveal the complete composition of the nail materials.Second, our sample set represents only a small proportion of the multitude of nail products on the market.Also, the glove penetration study included only three glove types and is thus suggestive of suitable gloves for nail work.
In conclusion, based on product analyses, we found that the labelling of artificial nail products was commonly incorrect or failed entirely to state the (meth)acrylate content of the products.Disposable neoprene gloves, when used for <20 min, probably provide protection against gel nail products whereas none of the glove materials tested could withstand acrylic nail liquid.Updating requirements for product labelling to clearly indicate the risk of sensitization associated with artificial nail products is urgently needed.
used as carrier gas in constant flow mode with flow rate of 1 mL/min.Sample injection into the GC column was carried out by direct vaporizing injection (splitless injection).The column oven final temperature was 280 C and inlet temperature 240 C. MS conditions were as follows: quadrupole temperature 150 C, ion source temperature 230 C, full scan mode in ion range m/z 30-400 with ionization energy of 70 eV.

Table 2
. The nail gel 'Mosaic Rubber Base Clear' (containing HEMA, HPMA, BDDMA, TREGDMA) penetrated the disposable nitrile and PVC gloves in 20 min test but not yet in 5 min.A very small amount of BDDMA was discovered to have penetrated in 1/3 parallel neoprene glove samples in 5 min but not in any of the 20 min' samples.The acryl nail liquid 'CND Retention + Sculpting liquid' (containing EMA, HPMA and HEMA) degraded the PVC glove within seconds.It penetrated the rubber gloves within 5 min, and we observed wrinkling of the materials already within the first minute of the test.The plastic film and the filter as such did not contain (meth)acrylates.