What it is
Pure metallic sodium is highly reactive and is never used as such in cosmetics, so the appearance of "Sodium" on a label generally reflects a labeling convention in which the sodium counter-ion of a salt or neutralized acid is listed. In practice the functional ingredient is the associated compound, such as a sodium salt of an acid used for buffering, chelation, or thickening. The role therefore depends on the parent compound rather than on sodium itself.
Safety & warnings
As a counter-ion present in common salts, sodium is not associated with irritation or sensitization at the levels found in cosmetics.
Questions everyone asks
Is this metallic sodium?
No. Metallic sodium is too reactive for cosmetics; on a label it typically reflects the sodium counter-ion of a salt.
What does it do?
Its function depends on the parent compound it is part of, such as buffering, chelating, or thickening salts.