The HEPA filter is made of non-toxic PP/PET material. A new filter may have a faint scent from the glue which is also non-toxic. After being used in the purifier for 2-3 days, this scent will fade away.
If the filter is left unused for a period of time with no wind passes through, the excessive moisture in the air will aggravate the breeding of bacteria, which produces acidic smell when turning on the model again.
In this case, you can turn on the machine and let the wind blow through several times, or put the filter under the sun for a few days. If all the above does not work, it is recommended to replace the filter.