Eosin 0.1%, aqueous is an aqueous solution of eosin, a water-soluble red dye used as a staining agent in histology and cytology. The 0.1% concentration is lower than that found in other commonly used eosin solutions, such as 0.5% or 2%.

The lower concentration of 0.1% eosin allows for more subtle staining and may be advantageous in certain situations when a more differentiated visualization of cellular structures or a weaker stain is desired. Eosin is often used in combination with other stains, such as hematoxylin, to highlight cell structures and extracellular components in tissues.

In general, eosin stains cell plasma and extracellular matrix components such as collagen fibers pink or red, while hematoxylin stains cell nuclei blue. The combination of eosin and hematoxylin, also known as hematoxylin-eosin (H&E) staining, is the most commonly used staining technique in histology because it provides a good overview of tissue morphology and organization.