Eosin Y is widely used as a biological stain in histology and pathology. It is particularly effective in staining cytoplasm, collagen, and muscle fibers, providing a pink to red contrast when paired with hematoxylin in the H&E staining method. This makes it invaluable for microscopic examination of tissue samples, aiding in the diagnosis of diseases.

In the field of cosmetics, Eosin Y is utilized as a colorant in lipsticks, blushes, and other makeup products, offering a vibrant red hue. Its ability to bind to proteins also makes it useful in the textile industry for dyeing silk and wool.

Additionally, Eosin Y serves as a fluorescent tracer in various scientific studies, including flow cytometry and fluorescence microscopy, due to its ability to emit light under specific conditions. It is also employed in photodynamic therapy for its photosensitizing properties, helping to target and destroy cancer cells when exposed to light.

In analytical chemistry, Eosin Y acts as an indicator in titration processes, particularly in redox reactions, due to its distinct color change properties. Its versatility across multiple industries highlights its importance as a multifunctional compound.