What are the consequences of under-fixation or over-fixation?

Insufficient fixation, or under-fixation, of a tissue sample can result in its degradation or putrefaction, making it unsuitable for mounting and staining by histologists for imaging. This can result in artifacts due to exposure to alcohol during processing or damage during decalcification procedures. 

Inadequate fixation, or delayed fixation, also results in a loss of antigenicity or the diffusion of antigens into surrounding tissues. 

Over-fixation can make the tissue brittle and difficult to handle during sectioning and staining. Additionally, it can lead to the masking of the epitope or cause strong non-specific background staining, which can obscure specific labeling. Over fixation also causes the loss of detectable staining signals.