In H&E staining, if ammonia is incompletely removed by washing, the outcome is:

• A. Poor staining with eosin
• B. Excess staining with hematoxylin
• C. Background eosin brightening
• D. Nuclei staining too dark

Answer: (A)

Residual ammonia leaves the tissue in an alkaline environment, which lowers eosin uptake. Eosin staining relies on a mildly acidic environment to bind cytoplasmic components effectively; when the section remains alkaline, the eosin cannot stain well, so the cytoplasm appears pale or poorly stained. The nuclei staining from hematoxylin would still occur, but the overall contrast is reduced because the eosin component isn’t properly staining. That’s why poor staining with eosin is the best explanation.