Negative ions are ions with a negative charge, that is, the charge carried by the electron is negative. Normal atoms or molecules are generally electrically neutral, meaning that they have an equal number of positive and negative charges. When an atom or molecule loses one or more electrons, it forms negative ions with a negative charge.

Hair is dry, short-tempered and even fried, because there are too many positive charges on the hair, and negative ions can neutralize positive ions, effectively close hair scales, and restore the silky luster of the hair.