One of the primary concerns with placing a heating pad on a mattress is the risk of overheating. Mattresses are often made from materials like foam or fiber that can easily retain heat. If a heating pad is left on for extended periods without proper monitoring, it can lead to overheating and potentially cause damage to the mattress or create a fire hazard. To mitigate this risk, it is advisable to use a heating pad with an automatic shut-off feature. These pads will turn off after a certain period, usually between 30 minutes to two hours, helping to prevent any overheating issues.