Modern society has several characteristics that distinguish it from the past. One of the most prominent concerns is the use of plastics. Plastics were first synthesized in the late 1800s and early 1900s, and their use exploded after World War II [1]. Lightweight, cheap, stable, and economical, plastics have become an indispensable part of modern society.

Microplastics are small pieces of plastic typically less than 5 mm in diameter. If the particles are smaller than 100 nm, they are termed nanoplastics. Recent studies have indicated the widespread presence of microplastics in organisms within marine ecosystems [2]. Accordingly, concerns about their health risks have continuously emerged. Previous studies supported the hypothesis that these exposures involve multiple toxic mechanisms. One study of microplastic exposure in rats found that the materials accumulated in the liver, kidneys, and intestines and measurably affected several biomarkers [3].

These experimental studies predicted that microplastic exposure is an ecological problem and could have direct human effects. Direct evidence of this hypothesis has emerged because microplastics can enter the human body directly through the consumption of food, including seafood and drinking water. Similar to that in other mammals, microplastic exposure can cause a range of toxic effects in humans.

The study by Leslie et al. [4] in 2022 was the first to reveal the presence of plastic polymers in human blood and quantify them. An association between the detection of microplastics in thrombectomy specimens and an increased risk of major cardiovascular events was recently reported [5]. This study is notable because it is the first to show a clear risk of disease directly attributable to microplastics over several years of follow-up. However, it is limited in that the study population was older adults; thus, future studies of such health effects across the life cycle are warranted.

Exposure to microplastics is particularly problematic in infants and children because their metabolic pathways differ from those in adults; moreover, the amount of exposure across their life cycle is expected to increase further for each passing generation. Accordingly, Chia et al. [6] comprehensively reviewed the health effects of microplastics with a focus on the expected effects in children. Similar perspectives were reviewed previously by other studies [7]. In that review, the authors identified a large knowledge gap in relation to infant and child exposure to microplastics and noted that very limited studies have focused exclusively on children.

The strength of this review is that it systematically presents the sources of microplastic exposure across the human life cycle. However, in terms of health effects, it still relies on experimental evidence. When translating the paragraphs on health effects in the Results, we noted that almost all of the evidence of health effects (mitochondrial damage, carcinogenicity, liver damage, respiratory system, endocrine system, etc.) cited in the review lacked sufficient epidemiological support.

Risk assessments consist of hazard identification, dose-response assessments, exposure assessments, and risk characterization. The current problem is that quantification methods to investigate the dose-response association and exposure assessments in humans have yet to be established. First, consensus is lacking about which biological samples can represent exposure to microplastics, although many studies have reported their detection in blood and tissues. Second, it is difficult to choose between spectroscopic methods (micro-Fourier infrared spectroscopy and Raman spectroscopy) and pyrolysis mass spectroscopic methods (pyrolysis-gas chromatography-mass spectrometry and thermal extraction desorption–gas chromatography/mass spectrometry) to measure microplastics in samples.

The strength of this review is that it describes the quantification of exposure assessments in detail. It is impossible to conduct a reliable epidemiological study without a reliable exposure assessment. Small research groups can use this as a guide to plan various pilot studies; however, national-level monitoring is required. The Korean National Environmental Health Survey, which has been conducted periodically since 2009, quantitatively assesses markers of exposure to several heavy metals and household chemicals [8]. The addition of a microplastics-related item to this program could be considered. Examples of suggested research topics based on current knowledge are listed in Table 1; however, further studies are needed to focus on measuring and quantifying microplastics in validated ways and determining which biological sample best represents the accumulated exposure.

As described above, the health effects of microplastics are expected to increase in the future. Some of the current surges in childhood illnesses compared to the past may be linked to microplastic exposure. Pediatric clinical professionals should be aware that microplastics may have a variety of effects on the human body and play a role in disease surveillance and the exploration of evidence at the frontline of clinical practice.