There was a belief that the breath of young women might be helpful in prolonging life. According to Mr. Wadd, one physician actually took lodgings in a girls’ boarding-school for this purpose. ‘I am myself,’ wrote Philip Thicknesse in 1779, ‘turned of sixty, and in general, though I have lived in various climates, and suffered severely both in body and mind, yet having always partaken of the breath of young women, wherever they lay in my way, I feel none of the infirmities, which so often strike the eyes and ears in this great city of sickness, by men many years younger than myself.’
~ T.H. White, The Age of Scandal
I can’t help wondering how diet, oral hygiene, and the presence or absence of halitosis factor in here, but I don’t expect that exhaling into the faces of old men is very beneficial for the young women in question. In fact it might be detrimental. Longevity studies have shown that lifelong bachelors (without, one supposes, easy access to the breath of young women) are more likely to die young. However, women living alone (who don’t, one assumes, regularly share their breath with men) tend to live longer than married women. Clinical trials may be in order.