We have a dog who is about 4 years old and has started losing the hair on her belly and underside of her legs. She is itching like crazy. We thought it might be the cedar shavings in her doghouse and got rid of these a few days ago. Any advice? Thank you very much.

At first glance it would seem that the problem you wrote about would be related to an allergic reaction, based upon the pattern of hair loss and pruritis (itching) you described.  Whether the problem has anything to do with the shavings would depend on the cause and effect relationship between the onset of the skin problems and the introduction of the shavings. 

History is always important in determining the likely causes for a problem.  Has the problem occurred before?  How long has the problem been present, and is it getting worse?  Are there other pets or people in the house that are affected?  Are fleas or ticks present?  Have there been any other changes in appetite, water consumption or weight?

If the problem occurred recently and for the first time, I would consider any changes that have recently occurred -- for instance, a change in bedding to the infamous cedar shavings, or perhaps you recently changed to a new diet.  If you can identify the offending change, simply reverse it and see what happens.  If there isn't a rapid improvement you should seek the attention of your local veterinarian.