How do you avoid catching the plague? Smoke constantly. Carry a sponge soaked in vinegar. Hang oranges studded with cloves around your house. This was the best medical advice available circa 1665, as the Great Plague ravaged London. The miasma theory of contagious disease held that sickness spread through unpleasant aromas. A whiff of ‘bad air’ could kill you – and the right fragrance just might save your life.