The 1% Alcoholic Eosin Solution is a histological staining solution containing eosin, a red dye, in an alcohol base. Eosin is a synthetic acidic dye that stains acidophilic (basic/eosinophilic) structures red. These structures primarily include cell plasma proteins, mitochondria, smooth endoplasmic reticulum, collagen, and keratin.

This solution is typically used to stain cytoplasmic and extracellular structures in tissue sections. In histology, alcoholic eosin solution is often used in combination with hematoxylin staining. Hematoxylin is a basic dye that stains acidic structures such as cell nuclei blue. Together, they form what is known as hematoxylin-eosin staining (H&E staining), which is one of the most commonly used staining methods in histology and pathology.

The alcohol-based eosin solution allows for better penetration of the dye into the tissue and can result in a shorter staining time. In addition, the alcohol base can help dehydrate the tissue during staining, which facilitates the further steps of tissue processing and embedding in kerosene.