The 28 1 on the mask was lost in July 2022, and the medical mask was produced in July 2022. Loss is the label of mask filter material, which means medical mask. July 2022 is the date of mask production, which is marked by the state regulations. When buying a mask, you can look at the product identification and packaging related information, mark the product name, trademark, model, implementation standard and other information on the product, and also mark the filter material grade.