Regumming may take place just to remove traces of mounting or to disguise more serious faults or repairs, in which case the whole stamp may be given new gum.
Such alterations are often easily detected with the naked eye due to differences in colour or texture between the old and new gum.
Another test is to use a magnifying glass to see if gum has gathered on the perforation edges of the stamp.
This means the gum is evenly distributed on the back of all the stamps contained on the sheet before perforating.
Also, when the stamps are torn to separate them from the sheets, fine tears along the perforation tips develop.