When a protein is denatured, why does it lose its functionality?

When a protein is denatured, it loses its functionality since its secondary and tertiary structures are modified. Although during denaturation, the protein retains its primary structures, it cannot serve its function since it needs all of its structural levels to do so. A protein can be denatured through several ways, such as, the addition of heat, a strong acid or base, or an organic solvent.