When it is an ion. You may recall from your high school chemistry class that ions are charged particles. They can contain a negative or positive charge, but it turns out that negative ions produce the most positive feelings.
When negatively-charged ions enter our bloodstream, they can increase the level of serotonin (the feel-good chemical) in our brains. This can raise our spirits, relieve stress, increase our energy and even reduce inflammation.
Now that you know that, it should come as no surprise that some of the best places to get negative ions are at the beach, beside a waterfall or in the mountains. So now you have another reason to get outside and commune with nature. It can literally make you feel better!