Coronavirus disease 2019 (COVID-19), which was caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was first identified in Wuhan City, Hubei Province, China, in late December 2019 and has spread rapidly around the world (1). As of 10 May 2023, more than 765 million people were infected, and more than 6.9 million people died as a result of COVID-19 infection, posing a great risk to public health (2, 3). Evidence demonstrates that the virus can infect through airborne transmission routes when an infected person ‘exhales, speaks, shouts, sings, sneezes, or coughs’ (4, 5), which makes the wearing of high-quality masks of particular importance in reducing COVID-19 transmission among the public (3, 4, 6–13). Although there is now substantial evidence for the effectiveness of wearing masks in mitigating the spread of COVID-19 (14–24), surprisingly little research attention has been paid to mask equity related issues such as the inequity in mask use (4) and the mask-wearing behavior associated with racial and ethnic disparities (25, 26). To date, no study has been done to investigate the disparities in the quality of masks associated with socioeconomic status.

When something appears to be so inexpensive that anyone can afford it (the mask costed about ¥0.20–¥0.50 a piece when we conducted this study) (27), people often ignore the inequality behind the product and may fail to recognize that such inequality exists, plus the fact that all masks look similar and it is hardly to tell the quality difference by naked eye. However, we believe that the invisible but serious inequity in the quality of daily-use masks exists. Because in our assumption, the rich (the monthly living expenses≥¥2000 in this study) may value the quality of the masks and do not care much about the price, while the poor (the monthly living expenses<¥1000 in this study) may be more concerned about money and tend to buy the cheapest masks among the already cheaper ones, and therefore use the low-quality or even unqualified masks. The invisible difference in mask quality can only be measured by using professional equipment to test their particle filtration efficiency. This kind of invisible inequality can lead to serious public health problems because the unqualified masks that the poor use cannot provide effective protection like authentic ones and may further increase the social health risk during pandemic (3).

In fact, the poor-quality masks circulating in the Chinese market has been a very serious problem since the COVID-19 outbreak. The poor filtration efficiency was the most important factor in the unqualified masks (28). By collecting the results of quality sampling inspection on masks conducted by China’s Administration for Market Regulation, we plotted the scatter of proportion of masks with unqualified filtration efficiency against sampling date, as shown in Figure 1A. As we can see from Figure 1A, the unqualified rate of masks before 2020 was very low, for example, in the national sampling of masks, there was no case of failure due to filtration performance. However, in the year 2020 when the COVID-19 pandemic broke out, the quality of masks available in China’s market became extremely poor, with the unqualified rate of mask filtration efficiency in various regions exceeding 40%, and even reaching 100%. After that, although the unqualified rate declined over time, by the end of 2021 when we conducted our research, the unqualified rate of masks in the national sampling inspection still reached 27.78%, and even at the end of 2022, the nationwide unqualified rate remained as high as 25%. To combat the low-quality masks and reduce the public health risk, the government may inspect mask quality in the market, however, which may not be always effective (3). As low-cost and low-quality masks circulate in the market, the quality of masks that people use daily may vary greatly. It is therefore important to find out whether the hidden socioeconomic inequality exists in mask quality and to make targeted policy recommendations.

This study aims to investigate the relationships between the quality of masks and family economic status. To achieve that goal, we distributed questionnaires to assess the participants’ characteristics including family economic status, and collected the participants’ new masks for daily use to measure the quality. By conducting fractional logistic regression and binary logistic regression with family economic status as core independent variable and the quality of masks as dependent variable, this paper contributes to filling the above-mentioned research gap by providing empirical answers to the disparity in the quality of masks and its relationship with family economic status. Family economic status was captured through examining the living expenses obtained from families. Quality of masks were measured from three aspects: the quality of filtration performance (including particle filtration efficiency, and whether the particle filtration efficiency is qualified), the quality of hygiene and cleanliness (whether the mask is individually wrapped) and the quality of aesthetics and design (whether the mask has the unique pattern or special design). We hypothesize that greater family economic status increases the probability of using masks with better particle filtration efficiency, the probability of using qualified masks, and the probability of using masks with individual packaging, and unique patterns and special designs.

We discuss our finding as follows. First, inequality existed in the quality of masks for daily use. The masks that used daily by Chinese college students had an average filtration efficiency rate of 0.891 ± 0.103 for 0.3 μm size particles, which was a little lower than China’s association standard for the civil sanitary mask (≥90% filtration efficiency for 0.3 μm particles) (78) and much lower than ASTM F2100 standard (≥95% filtration efficiency for 0.1 μm particles) (79). By the end of 2021, there were still a significant number (36.07%) of students using masks with filtration efficiency lower than the national standard with an average filtration efficiency of 0.795 ± 0.119, which indicated that the serious inequality behind the quality of masks cannot be ignored. Moreover, during the COVID-19 outbreak (from December 2019 to June 15, 2020), the severe facemasks shortage in China created a boom in counterfeit production, resulting in the low-quality of masks flooding the market during that time (3). Of the masks used daily by students with a clear date of manufacture, about 11.43% were manufactured during the outbreak with a relatively low average filtration efficiency of 0.819 ± 0.152, compared to 0.903 ± 0.081 for masks produced after June 15, 2020.

Second, our empirical results presented in Figures 3A–C demonstrated that the better family economic status was associated with a better particle filtration efficiency rate which means better-quality masks, which strongly confirmed our hypothesis. The fractional regression results of the full sample (Figure 3A) indicated that the masks used daily by students from average families and students from rich families had 1.188 and 1.441 times higher particle filtration performance than the masks used by students from poor families, respectively. The model constructed based on the perspective of whether the masks are qualified or not (Figure 3D) also confirmed our hypothesis, that is, the better family economic status was, the greater the probability for students to use qualified masks. The masks used daily by students from ordinary families and wealthy families were 1.339 and 1.751 times more likely to be qualified than those used by students from poor families. What worth noticing is that the most significant difference remains between the poor and the rich.

Third, our empirical results presented in Figures 3E,F revealed that the students who had better family economic status were more likely to use the masks with individual packaging, and unique patterns and special designs, which also strongly confirmed our hypothesis. This may not only lead to a de facto inequality in the quality of the masks used daily by the poor and the rich, but also lead to inequality on a psychological level, that is, the poor can clearly perceive that the masks they use are low-cost and not fashionable enough.

Additionally, in terms of control variables, the regression results of Changsha sample indicated that the religious beliefs had significantly positive effect on masks’ filtration efficiency, whereas the party membership had significantly negative impact on the filtration performance of masks. The root cause of this may still lie in the family economic status. Previous studies have found that, in China, family economic conditions were positively correlated with religious beliefs (80), and students from better-off families were significantly less likely to join the CPC (81). Also, the regression results of the gender variable (see Figures 3E,F) demonstrated gender differences in mask selection, with female preferring masks with aesthetics design over individually packaged masks. Besides, the older students also had a greater preference for individually wrapped mask that was clean and hygienic.

Although nowadays most people consider the masks as a cheap everyday item (27), there are still a significant number of people who are price-sensitive and using the cheap but low-quality or even unqualified masks. This kind of inequality is not easily visible, because it is difficult for us to see the differences in the actual quality of different masks with naked eyes. The results of our research underscore the importance of the government providing sufficient free qualified personal protective equipment to everyone without discrimination during the pandemic. Rapid global warming highly increases the risk of future emerging infectious diseases (82). COVID-19 will not be the last infectious disease event of our time (83); we need to prepare for the next challenge with sufficient necessary medical resources, especially the qualified personal protective equipment.

This study had some limitations. Although our results were based on a much larger sample size compared with previous studies (38), the convenience sampling method may still cause a potential selection bias (1, 84). Besides, the limited air flow rate (2.83 L/min) of our particle counter CEM DT9881 may lead to some limitations in testing accuracy. Also, in an anonymous questionnaire, misrepresentation is inevitable, but we have minimized its impact on our study findings. Since we conducted the survey through teachers and counselors whom the students were familiar with, which means that we had the trusting endorsement from the teachers and counselors, so the students might be more willing to respond honestly to sensitive personal questions such as income level and family background.

Our analysis reveals the hidden socioeconomic inequality that exist behind the seemly cheap masks, and the family’s economic status was positively correlated with the quality of masks. The findings of this study have important implications for public health policy makers particularly those addressing future infectious disease control. In facing the challenges of future emerging infectious diseases, it is important for public health departments to address the inequity to ensure equal access to affordable qualified personal protection equipment.

To the best of our knowledge, this is the first article to evaluate the quality of masks in Mainland China based on a large set by testing their filtration efficiency for airborne particles, and the first empirical study to investigate the relationship between the quality of masks and family economic status.

There are still many questions that need to be further discussed. This study provides a starting point for future research. The following questions can be considered: Can this inequality phenomenon be observed in other general groups or other countries? In addition to the family’s economic status, do other socioeconomic factors such as occupation and social class also have a notable impact on the quality of masks? How does socioeconomic status influence people’s masking behavior, such as whether they choose to reuse the masks and the frequency of changing a mask?

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by the School of Public Administration, Nanfang College · Guangzhou. Written informed consent from the participants’ legal guardian/next of kin was not required to participate in this study in accordance with the national legislation and the institutional requirements.

LH conceived of the study, conducted the survey, evaluated the quality of masks, collected and analyzed the data, and prepared the manuscript draft. YiW provided comprehensive editing and refinement of the manuscript. BM, ZG, YuW, ZS, MH, HC, XM, and JX conducted the survey and collected the data. ML collected some additional mask samples and provided language editing of the manuscript. All authors contributed to manuscript revision, read, and approved the submitted version.

This study was supported by the Young Innovative Talents Project of Colleges and Universities in Guangdong Province (2018WQNCX280) and School-level Research Projects of Nanfang College · Guangzhou (2021XK10).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.