The present paper examines whether there exists a change in the concentration of carbon dioxide that is trapped in the surgical facemask during the procedure of respiration and whether the results of the sequestered CO2 can have harmful effects on the human organism. In order to answer the research questions, an experiment has been designed and implemented, with the use of an Arduino microcontroller (Arduino UNO) and a gas sensor (MQ-135). The experiment was conducted by measuring the exhaled CO2 concentration level using an appropriate experimental layout—at first without a surgical mask and then while wearing one. This procedure is repeated three times; therefore, the experiment is divided into three stages. In every stage there is change as far as the respiration method is concerned: first, the measurement takes place without the ongoing use of a surgical mask, then while wearing it, and finally while wearing it after 45 min of use. According to the results of the experiment, there is an observation of sequestration of carbon dioxide trapped in the mask.