What are the possible causes for nonspecific or diffuse bands for my western blot experiment?

Possible cause 

Solution 

Excessive amounts of protein loaded on gel

Load less sample on the gel

High antibody concentration 

Use a lower concentration of antibodies, particularly for primary antibodies 

Chemiluminescent substrate emits a very strong signal

• Use a less concentrated substrate
• Reduce duration of membrane incubation with substrate
• Expose blot to film for a shorter duration
• Use a lower antibody concentration, particularly AP- and HRP- conjugated antibodies
• Remove substrate completely after incubation is complete