A lot of people give the same reason for an answer on here. The Real question Should be... WHY, is it overheating? The Answer is simple... either people don't bother to clean off the outer and Inner air intake screens (like on the Conair's), or, over time... dust and other tiny debris build up within the "tunnel" where the heating element is, thereby restricting the airflow which causes an excess buildup of heat, that it cannot get rid of, due to restricted airflow.
Either way... a clogged air intake screen (most likely culprit) or a clogged heating element "tunnel" restricts airflow past the heating element, causing excess heat.
One way to easily know if it's in the heating/exhaust "tunnel" is... the air will have a "burnt" smell to it.
If it's a clogged air intake screen.. there will be a noticeable reduction in airflow.... CLEAN the air intake screens... it's very simple, if not... then read your Owners Manual on "how to" maintain your dryer... it's Not "rocket science". : )