Chips and hard drives use electricity and generate heat that can damage circuit inside the system. Laptops are smart enough to shut down itself when it gets too hot and protects itself from permanent damage. A system that shuts down itself may cause less evil and it is something that you should avoid. Heating problems are nothing but ventilation problems.
Make sure that there is no blockage of vents on the side. Do not put a running laptop on a cushion, pillow or bag. You may do this safely only if your system is off, hibernated or in sleep mode. If the problem continues, buy a laptop cooler. The pads that are underneath the laptop whisk away the heat. Some laptops also have fans. Further contact nearest dell service center for better assistance
It is more difficult to clean a laptop compared to the easy to open desktop tower. Rather than compressed air, blow the dust deeper inside your system, use a small vacuum for sucking dirt from the vents. You may turn the laptop over and look for screws for removing. Be very careful while accessing the RAM and hard drive and clean its surroundings.
Most laptops use fans for circulating air through the case for bringing down the temperature. If your system gets hot too often, block the ventilation. Using laptops is more challenging as it produces less heat and is packed tightly. This creates more ventilation problems and is more difficult to get into. Only professionals should open the main body of the laptop for cleaning purpose. So contact service centers if you face any such issues.