Radiotherapy or chemoradiation to the head or neck can affect your salivary glands. This means that you may not make as much spit (saliva) as before and so your mouth may become dry. Your salivary glands may gradually recover after treatment finishes, but your saliva may be thicker and sticky. Some people have a dry mouth permanently.
If you feel you have too much saliva rather than too little, this may be a sign of swallowing difficulties.