Without knowing the enviromental conditions of the animal in question,it is allmost impossible to say for sure what is hapening.
It could be as simple as a cloged nostril,or it could be stress from improper conditions,or the early stages of a RI.
As Mary said a trip to the vet should be made,and in the meantime a couple of thermometers and a humidity gauge would help greatly .You can be sure that the vet will ask how the boa is being kept and not knowing the exacts of the enviroment is not going to help much with the assesment.
Good luck and keep us informed