One cause of uneven staining of the H&E may be water contamination of the clearing agent on the processor.

• A. True
• B. False
• C. Contamination of dehydration agent
• D. Contamination of embedding medium

Answer: (A)

Uneven H&E staining often starts with the clearing step, which swaps ethanol for a clearing agent that prepares tissue for paraffin infiltration. The clearing agent must be anhydrous. If water contaminates the clearing agent, it can’t fully displace residual water and ethanol in the tissue. This leads to incomplete clearing and uneven paraffin infiltration, creating micro-regions that differ in how they take up hematoxylin and eosin. The result is patchy or variable staining across the section. While contamination of dehydration agent or embedding medium can cause artifacts too, their primary effects aren’t as directly tied to the clearing step’s role in enabling uniform dye uptake, making water in the clearing agent a plausible and common cause of the uneven staining.