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