My husband drives me mad constantly clearing catarrh from his throat - he's done it for years, even when he hasn't got a cold. He doesn't smoke or suffer from allergies and is fit and well. Is there any remedy to clear it up?

It sounds as if he has a 'post-nasal drip' - that is, excessive mucus production at the back of his nose. This can come from a chronic inflammation in the post-nasal space, or from his adenoids, or both. He needs his doctor to look at his nasal airways, to determine the state of his mucous membranes, the width of the air passages, and whether they are swollen, or have polyps in them. Treatment may involve a simple intranasal spray or surgery, depending on the cause. But he shouldn't leave things as they are.

I have been exercising twice a week for the past year and I'm convinced I'm getting far fewer colds than I used to. Is this wishful thinking, or is there compelling evidence that exercise can boost immunity?

I'm sure that exercise is making you healthier and fitter, but I'm not convinced that it has changed your immune system. The number of colds we have varies over our lifetime. We start catching colds as toddlers and continue well into our 20s. By that time we have become immune to a fairly high percentage of the cold viruses we come up against, so we have fewer. Often our middle years are virtually cold-free because of that. Starting to exercise probably coincides with your rising resistance to the current cold viruses. As for exercising improving immune systems, I don't know of good prospective trials to prove this one way or another - I'd like to hear from people who do know of them.

Why do I always get excess saliva in my mouth either when I feel nauseous or just before I'm sick - is there a physical reason for the body to produce it?

In any kind of nausea, part of the process is stimulation of the salivary glands in the mouth and of the mucus-secreting glands in the stomach. That is why you get a lot of saliva before vomiting. In Scots we call that a 'wet boak'. The saliva may be a mechanism to protect the mouth and upper oesophagus by diluting the acid and pepsin (a protein-digesting enzyme) that makes up a large part of the material rising up from the stomach.