Every morning, regardless of season or health, my wife's nose starts to run the moment she wakes up and continues for about two hours. She also tends to sneeze a couple of times upon being presented with a cup of tea. Why does this happen?

Why does pulling out your nasal hairs make your eyes water in a way that a similar level of pain elsewhere on your body wouldn't?

Alan Williams, Edinburgh, UK

Our smelling sensors are inside the head. Our noses are vulnerable to damage and the majority of primates and other mammals manage with relatively flat faces.

Dennis Newland, Purley, Surrey, UK

I have attended several different types of exercise class over the years, and I'm always instructed to breathe in through the nose and out through the mouth while exercising. No instructor can tell me why.

Is there a scientific reason for this advice?

Heather Shute, Oxfordshire, UK

Eating a roast beef and mustard sandwich is one of life's simple pleasures* - except for when the mustard flavour seems to go up your nose to create a horrible burning sensation! 

I get the same effect from horseradish too - but nothing else causes this when I eat - it is unique to those two condiments...and can be almost painful!

Can anyone explain what is happening here?

* apologies to vegetarians - cheese and mustard/horseradish instead?

Angela Hsu, University of Otago, Dunedin, New Zealand

I noticed it first when I had a sandwich that had some tomato relish in it. As soon as I brought the sandwich to my mouth to take a bite, I immediately got a strong smell of acetone - at least that is the closest smell I can think of. It didnt smell like any kind of food and I couldnt smell it for long without having to take it away again it was so strong. I decided then that there was just something wrong with the sandwich. But later when I was chopping tomatoes I got the smell again, so I decided to test with a few other items - ketchup was the only other thing I had that gave me the same smell. I tested them and no one else smelt anything out of the ordinary. So presumably it was caused by some mucus in my nose at the time. Was it a chemical reaction in my nose that caused the strange smell?

2 days later and tomatoes smell normal again - the strange thing is, I still have a cold.