What are the precautions or limitations when using propidium iodide?

There are several important precautions one should be aware of  when using Propidium iodide. Propidium iodide is only able to penetrate the membranes of dead cells, and should not be used in experiments for staining viable cells. PI is also widely used in conjunction with Annexin V to assess if cells are viable, apoptotic, or necrotic through differences in permeability and plasma membrane integrity; PI on its own can only indicate cells that are in necrosis. Additionally, it has been shown that PI staining of adherent cells in biofilms may significantly underestimate bacterial viability because of the presence of extracellular nucleic acids. PPE procedures for handling PI should also always be followed to avoid over exposure. One should wear gloves, goggles, a lab coat, and avoid any direct contact or inhalation with the chemical. This includes working in the fume hood to avoid exposure.