Skin irritancy generally increases in the series non-ionic, amphoteric, anionic, cationic surfactants. Long-chain alkyl amine oxides are used as amphoteric surfactants and foam stabilizers. Zwitterionic (amphoteric) surfactants have both cationic and anionic centers attached to the same molecule. Subsequent investigators reported iodine-like, cationic, or amphoteric behavior. Gallium hydroxide, which is amphoteric, also dissolves in alkali to form gallate salts. Arsenic trioxide is an amphoteric oxide, and its aqueous solutions are weakly acidic. Beryllium hydroxide is an exception as it exhibits amphoteric character. The oxide SbO is polymeric, amphoteric, and a glass former. The oxide GeO is polymeric, amphoteric, and a glass former. The oxide AsO is polymeric, amphoteric, and a glass former. Biological amphoteric molecules such as proteins contain both acidic and basic functional groups. The hydroxide of astatine At(OH) is presumed to be amphoteric. Aluminium hydroxide is amphoteric in nature, i.e., it has both basic and acidic properties. Bendamustine is a white, water-soluble microcrystalline powder with amphoteric properties. There are also amphoteric exchangers that are able to exchange both cations and anions simultaneously.