Alcian Blue 1 % (pH 2.5 in acetic acid) is a special staining solution used in histology and cytology. This aqueous solution contains 1% Alcian Blue, a cationic dye that specifically binds to acidic polysaccharides found in various tissues such as mucus, cartilage and other extracellular matrix components. Staining occurs at a pH of 2.5, which increases the dye's selectivity for sulfated glycosamine glycans and acidic mucopolysaccharides.

Alcian blue staining is particularly useful for distinguishing and characterizing mucus structures and for observing changes in mucus production that may be associated with certain disease states. It is also used in combination with other staining methods to provide a differentiated picture of tissue structure.