hot MacBook

In the last couple of months our two-year-old MacBook has been running hotter than before. I do not yet have any data to present here (although I can later.) For the moment I can report that the lower case gets warmer than we are accustomed to, and the fan becomes audible. I don't think that the situation is caused by the applications; when this last occurred I was using only Safari, and I was on a website without any video content.

We are not putting the MacBook on pillows. We have it on flat surfaces, like a table top.

I have seen this heating problem with laptops before. With the iBook I saw online recommendations to vacuum the ventilation ports. I have not seen any similar instruction for the MacBook.

I have to think that any computer would get dirty in two years. My first thought is that, as with the iBook, perhaps the MacBook needs cleaning. Is that possible?

Or is there something else we need to know about the MacBook?