Is it true that bald men have higher male sex hormone levels than men with a full head of hair? And does that make them more susceptible to heart attacks?

The accepted story is that baldness is related to the male sex hormone testosterone, but there's little evidence that the average bald male is any more sexually active or aggressive than his hairy counterpart. As for a higher risk of heart attack, that's definitively ruled out by a study of more than 5,000 men, about half of them bald. There was no difference between the two groups in their histories or risks of heart attack. So baldness is neither a risk factor for heart disease, nor a sign of extra masculinity. Sorry, gents (from a male with a near-full head of hair).

I often have a cold immediately after a long-haul flight. Is it true that the conditions in planes are ideal for spreading viruses, and that we will all catch an infection if just one other passenger sneezes?

No, that isn't true. A recent study in Annals Of Occupational Hygiene sampled the air in planes in level flight, during boarding and after landing. It contained no germs, bacteria or viruses that would cause colds or chest infections. Tests of the air filters didn't find them, either. The only germs detected were those usually found on the skin, in dust, or as common organisms in average samples of air taken routinely outdoors. In fact, during the flight, the air was purer (ie, contained fewer organisms) than air sampled from offices.

· Do you have a question for Dr Smith? Email doctordoctor@theguardian.com