In the case of amphoteric surfactants, the hydrophilic part of the molecule has both a negative and a positive charge, which neutralize each other. Depending on the structure, these can be located and stabilized at different densities in the molecule.
Depending on the pH of the formulation, some of the amphoteric surfactants in their charge may be affected. Acid formulations can cause a charge shift in the positive range. The surfactant then behaves in the same way as a cationic surfactant.
In another case, the base environment can lead to a negative charge shift, the surfactant will behave in the same way as an anionic surfactant. In combination with anionic surfactants, amphoteric surfactants have a thickening, foam-enhancing / stabilizing effect and can improve skin tolerance.
They are often used as co-surfactants to take advantage of synergistic effects, to condition surfaces or, for example, to reduce the static build-up of hair.