Arduino heating problems

I am supplying power to Arduino from a 12V adapter. The board gets heated too much after few hours. For my project I wont need a battery source, the board is constantly supplied from adapter. But I want it to run continuously for several months. So does this heating of arduino damage it. If so, how long will it last? How do I estimate this on a paper?

Does putting arduino to sleep reduce this problem?

Thanks in advance.

arduinofresher:
I am supplying power to Arduino from a 12V adapter. The board gets heated too much

Does putting arduino to sleep reduce this problem?

Probably not much. The real problem is that you are using pretty crude regulators and you are leaning 12v against them. A 12v supply is at the upper recommended limit and should be kosher. A 9v adapter will make both you and Arduino feel somewhat more comfortable, but even they throw a lot of heat out. My project runs for months on 9v. I would not use 12v, no matter what the book says.

Ok. I will change the adapter to 9V one. Thanks for the reply.