Sniff some lavender or rosemary. The scent of lavender can bring you a restful night’s sleep, but the plant can do you a world of good in daylight, too. In a recent study, volunteers sniffed the essential oils of lavender or rose mar for 5 minutes. The Results; Levels of the stress hormone cortisol in saliva dropped by as much as 25 percent. That’s good, because the hormone increases blood pressure and suppress the immune system. What’s more, people who smelled low concentrations of lavender or high concentrations of rosemary were better at getting rid of free radicals, the pesky molecules believed to speed aging and disease.