Evaluating paraben concentrations in skincare products and assessing their potential health risks

Chemicals and SCPs

All chemicals used in this study were of analytical grade. The solvents, including ethyl acetate, methanol, acetone, iso-octane, and acetonitrile, were obtained from Fisher Scientific (Pittsburgh, PA, USA). The paraben compounds (i.e., MeP, EtP, and PrP) were acquired from AccuStandard (New Haven, CT, USA) in more than 97% purity.

The SCPs examined in this study were sourced from the personal collections of female staff members at the King Faisal Specialist Hospital and Research Centre. These staff members contributed a total of 111 products from renowned brands. The various product types included the following: 100 hand/body creams or body lotions, five gels, three ointments, two cleansers, and one hand balm. Except for the cleanser, these products are categorized as leave-on and are designed for prolonged skin contact. Three products were manufactured in Saudi Arabia, while the others were imported from other countries, such as the USA, Germany, Thailand, France, Canada, and India. Six products differed in batch numbers and/or countries of manufacture despite sharing a brand name. All products were stored at room temperature (~22-25 °C) until analysis.

Sample preparation

A 7 mL solvent mix (i.e., ethyl acetate, methanol, acetone in a 2:4:4 ratio) was added to 0.05 g of each SCP sample and vortexed for 1 min. Subsequently, the samples were ultrasonicated for 30 min to facilitate the extraction of preservatives, followed by centrifugation at 3,000 rpm for 20 min at a temperature of 20 °C. The resulting supernatants were diluted with deionized water. In the purification process, C18 cartridges (500 mg, Varian Inc., USA) were preconditioned by sequentially passing solvents in the following order and volumes: first, 2 mL of iso-octane to remove hydrophobic impurities, followed by 2 mL of ethyl acetate and 2 mL of methanol to ensure the removal of less hydrophobic compounds, and finally, 2 mL of deionized water to equilibrate the cartridge for aqueous sample loading. Subsequently, preconditioned cartridges were loaded with the diluted supernatants, and the cartridges were eluted using 1 mL of 50% acetonitrile. Finally, the eluate was evaporated to dryness using nitrogen gas. Subsequently, the resultant dry residue was reconstituted in 200 μL of acetonitrile for further analysis.

Chromatographic analysis

The paraben compounds were quantified with an Alliance Waters HPLC 2,695 system equipped with a multiwavelength ultraviolet (UV) detector, Model 2,487 (Waters Corporation, MA, USA). Chromatographic separation was achieved using a Zorbax SB C18 column (12.5 mm × 4.6 mm) with a 5 µm particle size (Agilent Technologies, USA). A Waters Symmetry™ C18 guard column (4.6 cm × 2 cm; 5 µm particle size) filled with the same type of C18 silica-based packing material as the analytical column to protect it.

A Dell Optiplex GX1 computer with Millennium32 software (Waters Corporation, MA, USA) was used for data acquisition and system operation. The injection volume was 10 µL. A UV detector 2,487 with an Alliance 2,695 system from Waters was used for detection, and the excitation wavelength was set at 254 nm. The chromatography was performed using an isocratic mobile phase consisting of a mixture of acetonitrile and water in a 40:60 v/v ratio, with a flow rate of 1 mL/min. The retention times were as follows: 5.4 min for MeP, 7.8 min for EtP, and 12.3 min for PrP. The total analysis cycle time was approximately 14 min.

Validation study

Calibration curves were established by measuring paraben compounds in the SCPs for six concentrations. In the calibration phase of our analysis, six SCP aliquots were spiked with a stock solution of each paraben, resulting in concentrations of 1, 2, 4, 8, 16, and 32 µg/g wet weight. All stock and calibration solutions were prepared using acetonitrile as the solvent to ensure the consistency and reliability of paraben concentration measurement. During quantification, the peak heights of each compound were plotted against their respective concentrations using the least-squares regression method. Calibration curves derived from six individual runs exhibited a strong linear relationship. The coefficients of determination (r² values) were 0.9972 ± 0.0025 for MeP, 0.9985 ± 0.002 for EtP, and 0.9981 ± 0.002 for PrP, indicating excellent model fit as they explained over 99% of the variance for each compound.

The spiked samples were subjected to standard extraction and analyzed to determine recovery rates. The results indicated high analytical recovery across all tested concentrations: MeP recoveries were 96%, 94%, and 87%, with relative standard deviations (RSDs) of 15%, 8.5%, and 10.4%, respectively. EtP recoveries were 96%, 93%, and 91%, with RSDs of 10%, 6%, and 9.6%, respectively. PrP recoveries were 93%, 89%, and 108%, with RSDs of 10%, 9.9%, and 9.7%, respectively. These findings demonstrate the robustness and reliability of the extraction method at various concentration levels.

The method detection limits (MDLs) and limits of quantitation (LOQs) for each paraben were established following procedures outlined by the US Environmental Protection Agency^[17]. For each compound, 10 samples were processed through the entire analytical method. The MDL was calculated using the formula: MDL = t (n - 1, α = 0.01) × s. Here, n is the number of replicate analyses; s is the standard deviation of the replicate analyses; and t is the Student’s t value for (n - 1) degrees of freedom at the 99% confidence level. The LOQ was determined as LOQ = 10 × s. The calculated MDLs were 0.0004, 0.00043, and 0.00023 µg/g for MeP, EtP, and PrP, respectively. The corresponding LOQs were 0.004, 0.0043, and 0.0023 µg/g for MeP, EtP, and PrP, respectively. The results are reported in g/kg. The sum concentration of the three parabens was denoted as Σ₃parabens.

Frequency of parabens in SCP

In this study, 111 SCPs were analyzed to detect three common paraben compounds (MeP, EtP, and PrP). Figure 1 graphically represents the percentage of samples containing each paraben type. MeP was the predominant SCP; it was present in 77% of the samples. PrP and EtP were present in 63% and approximately 30% of the samples, respectively. Detailed information, including specific brand data, is provided in Table 1. The widespread use of MeP is reflected in Figure 1 and Table 1, demonstrating its dominance due to its broad-spectrum antimicrobial activity, stability, and cost-effectiveness. Additionally, 13.5% of the analyzed products were paraben-free, indicating a growing market trend toward “paraben-free” formulations driven by consumer concerns about potential health risks.

Figure 1. Bar chart showing the percentages of MeP, EtP, and PrP detected in 111 SCPs. The Y-axis represents the percentage of samples in which each type of paraben was detected, clearly indicating that MeP is the most prevalent, followed by PrP and EtP. MeP: Methylparaben; EtP: ethylparaben; PrP: propylparaben; SCPs: skincare products.

The preservative efficiency of parabens depends on their alkyl chain length. Longer chains imply a higher antimicrobial potency but lower solubility. Thus, products often use a mix of short- and long-chain parabens^[18,19]. In our study, Σ₃parabens (i.e., a combination of three different parabens) were found in 86.5% of the products, while 20.7% of the products contained only one type of paraben. The highest median concentrations were 0.813 g/kg MeP and 0.08 g/kg PrP. In general, these values were much higher than those reported by Li et al. (0.0475 g/kg of MeP and 0.0022 g/kg of PrP) but lower than those reported by Guo et al. (2.8 g/kg of MeP and 1.56 g/kg of PrP)^[20,21].

The EU Regulation 1223/2009 on cosmetic products limits the total paraben concentrations in cosmetics to 8 g/kg, with no single paraben allowed to exceed 4 g/kg^[13]. These limits are deemed safe for small-molecule parabens, such as MeP and EtP; however, the Safety Committee on Consumer Safety set a stricter limit of 1.4 g/kg for longer-molecule parabens, such as PrP, in cosmetics owing to concerns about their potential endocrine-disrupting effects^[12]. Our study found that MeP and EtP concentrations exceeded safety limits in nine and three SCPs, respectively, with concentrations exceeding 4 g/kg. Additionally, 19 SCPs surpassed the stricter limit for PrP. Moreover, six products containing all three parabens (Σ₃parabens) had MeP and EtP concentrations above 8 g/kg.

Daily exposure to parabens

Parabens can be absorbed through the skin during SCP application, possibly leading to systemic absorption that increases when applied to damaged skin^[22]. A recent study showed that dermal exposure to MeP, EtP, and PrP from cosmetics leads to a long half-life, with only 1.7%-2.3% excreted in the urine^[23]. We calculated the estimated daily intake (EDI) of parabens via dermal contact based on the formula proposed by Guo et al.^[21]:

where
· f1 is the retention factor, which indicates the proportion of parabens remaining on the skin after application;
· f2 is the dermal absorption factor, which quantifies the extent to which a substance is absorbed through skin contact;
· Cs represents the concentration of parabens in the product (mg/kg);
· DM is the mass of the product applied to the skin (kg);
· BW is the body weight of the individual (kg).

The EDI, expressed in micrograms per kilogram of body weight per day (μg/kg-BW/day), quantifies either the intake of an individual paraben or the cumulative intake of up to three different parabens. This calculation utilizes the specific paraben concentration in SCP (Cs, μg/g) and the daily usage rate of these products (DM). For example, the daily application of body lotion is estimated at 8.69 g per day, based on data from the USEPA^[24].

The retention factor (f1), which is the fraction of the product remaining on the skin after application, was assumed to be 1 for body and hand lotions, as per Wormuth et al.^[25]. The dermal absorption factor (f2), which indicates the amount of paraben penetrating the skin, varies between 15% and 75%^[26]. We used the higher end of this range (75%) in our estimates while calculating skin penetration.

We also considered the average body weight of Saudi women over 18 years old (68.8 kg), as reported by Al-Saleh et al.^[27]. Accordingly, the mean (and maximum) EDI values for MeP, EtP, and PrP were 128.8 (1,412.6), 29.96 (1,341), and 53.97 (285.7) μg/kg-BW/day, respectively. The dermal exposure doses of MeP were more than twice those of PrP. The European Food Safety Authority (EFSA)^[28] set an acceptable daily intake (ADI) limit of 0-10 mg/kg-BW/day for the sum of MeP, EtP acid esters, and their sodium salts. This limit was derived from the no-observed-adverse-effect levels (NOAELs) established at 1,000 mg/kg-BW/day for each compound. These levels are based on long-term toxicity studies and research focusing on sex hormones and their impact on male reproductive organs in juvenile rats, as reported by EFSA^[28]. Notably, PrP was not included in this assessment because of insufficient NOAEL data at the time. However, the proposed ADI for PrP of 100 μg/kg BW/day was derived from a NOAEL of 100 mg/kg-BW/day^[29,30].

Our study found that the maximum combined EDI for MeP and EtP (2,753 μg/kg-BW/day) was approximately four times lower than the ADI limit, even with a 75% dermal absorption rate. In contrast, the EDI of PrP in 26 (23.4%) of the products exceeded the recommended ADI, with the highest calculated EDI being approximately thrice the ADI. While our findings suggest that the presence of MeP and EtP in the tested SCP poses a low health risk, the detection of PrP in 26 products raises concerns. Honda et al. conducted a biomonitoring study measuring six paraben congeners in 30 urine samples collected from Saudi Arabia and calculated the EDI (μg/kg-BW/day); the values decreased in the following order: 1.3 (MeP), 0.19 (PrP), and 0.05 (EtP)^[29].

Health risk assessment

Given that individuals are often exposed to multiple parabens simultaneously, the hazard quotient (HQ) was calculated for each specific paraben. The HQ reflects the ratio of the EDI to the ADI, where the ADI represents a threshold dose below which no adverse effects are expected^[31]. To assess the cumulative risk from exposure to various parabens, we utilized a hazard index (HI). The HI aggregates the HQ values for three specific parabens: MeP, EtP, and PrP^[32]. An HQ or HI exceeding 1 indicates that exposure levels have surpassed the acceptable dose for a single paraben or the cumulative exposure to all evaluated parabens, respectively. In our study, the HQ for PrP in 26 SCPs exceeded the safe limit, with values ranging from 1.03-2.9. The average HI for the three parabens was 0.55, indicating a generally safe level across the product range, but 26 SCPs, particularly lotions and creams, had an HI greater than 1.

The margin of exposure (MOE), a metric employed to evaluate the risk related to the presence of parabens in personal care products, was calculated as the quotient of the toxicological NOAEL value and EDI^[33,34]. The formula for calculating MOE is as follows:

where
· NOAEL: The highest exposure level at which no adverse effects are observed, typically measured in mg/kg-BW/day.
· EDI: The estimated daily intake of parabens through dermal absorption, expressed in μg/kg-BW/day.

The NOAEL values were set at 1,000 mg/kg-BW/day for MeP and EtP, and 100 mg/kg BW/day for PrP, following previous studies^[28-30]. An MOE greater than 10,000 is generally considered safe, indicating a low level of health risk^[33]. However, as illustrated in Table 2, none of the SCPs analyzed in this study achieved the safety threshold of an MOE exceeding 10,000. This finding suggests that even products traditionally considered safe based on dermal exposure assessments may pose potential risks if used frequently. Tokumura et al. reported that an MOE for PrP below the threshold signifies a high risk of disruption of the reproductive system^[35]. These findings suggest that a potential health risk is associated with exposure to these specific products, primarily due to PrP, especially with frequent use. Notably, paraben exposure can also occur through other routes, such as food intake and inhalation of indoor air, medicines, and dust, which could further exacerbate the potential for health risks.

Study limitations

This study has certain limitations. First, this study focused on emulsion-based products such as creams and lotions. Hence, paraben exposure from other product types, such as gels, serums, or sprays, may not be fully captured. Future research should include a wider variety of skincare formulations to provide a more comprehensive understanding of exposure and health risks across diverse product categories. Second, the EDI for parabens was derived using hypothetical daily urinary volumes for a female subject, possibly introducing additional variability. This methodological choice, combined with the exclusion of metabolites, may affect the accuracy and reliability of our exposure assessments. This limitation underscores the need for more precise data collection and analysis methods in future studies. Third, the SCPs were exclusively collected from female staff members, limiting the generalizability of the results. Fourth, the parabens in urine samples were not analyzed. Future studies should include such analysis for a more thorough risk assessment of human exposure to parabens. Fifth, our estimates may not fully capture the actual paraben exposure levels, as the analysis was limited to the measurement of only three congeners. Finally, owing to the lack of specific dermal absorption factors for each paraben, a uniform percentage absorption rate of 75% was assumed for all parabens. Hence, the estimated EDI values may differ from the actual exposure levels.

Conclusion

In this study, 111 SCPs were analyzed. The analysis revealed a concerning prevalence of MeP, EtP, and PrP. Several products contained MeP and EtP concentrations exceeding the safety limits prescribed by the European Union. More alarmingly, an even higher number of products surpassed the stricter limits for PrP. Furthermore, our health risk assessments indicate that many of these SCPs may pose potential health risks to consumers. Given these findings, it is crucial for consumers to be informed and alert. We recommend that consumers preferentially select products that are free from parabens or those that contain safer alternatives, thereby minimizing their exposure to these potentially harmful chemicals. Retailers and manufacturers can support this shift by clearly labeling paraben contents and promoting paraben-free options. For policymakers, this study underscores the need to establish stringent, evidence-based regulatory limits on paraben concentrations in consumer products. It is advisable to tailor these limits according to local usage patterns and product types to enhance consumer safety effectively. Regulatory bodies should also consider enforcing stricter disclosure requirements to ensure transparency about the paraben content of consumer products. By adopting these recommendations, consumers and policymakers can contribute to a safer, more informed marketplace, ultimately protecting public health.