H&E  and PAS are the two most commonly used stains in histopathology.

Haematoxylin and eosin (H & E)

This is the most commonly used stain in routine pathology. Haematoxylin, a basic dye stains acidic structures a purplish blue. Nuclei (DNA), ribosomes and rough endoplasmic reticulum (with their RNA) are therefore stained blue with H&E. Eosin, in contrast is an acidic dye which stains basic structures red or pink. Most cytoplasmic proteins are basic and therefore stained pink or pinkish red. In summary, H&E stains nuclei blue and cytoplasm pink or red. The following specimen shows a normal skin stained with H&E.

 

PAS (periodic acid-Schiff)

This stain is versatile and has been used to stain many structures including glycogen, mucin, mucoprotein, glycoprotein, as well as fungi. PAS is useful for outlining tissue structures--basement membranes, capsules, blood vessels, etc. As it stains many structure; this can give rise to a high background. It is very sensitive, but specificity depends upon interpretation. The following specimen is a normal cornea that has been stained with PAS and the basement membrane of the epithelium is highlighted.