This is common knowledge of electricity, and junior high school physics has this knowledge, which belongs to friction electrification.

In a dry environment, the friction between plastic and hair will produce electron transfer, which will make the plastic comb charged. Wearing an electronic comb will attract hair and let it float with the comb.

In wet weather, the friction between the comb and the hair will also make the comb charged, but because the wet air is conductive, the electrons brought by the friction between the comb and the hair are released through the wet air, and the comb loses its electrons and is no longer attractive to the hair, so the hair will not float. ...