The neurological studies of music on the brain seem to indicate that we're hardwired to interpret and react emotionally to a piece of music. Indeed, this process starts very early on. One study found that babies as young as five months old reacted to happy songs, while by nine months they recognized and were affected by sad songs [source: LiveScience]. Physiological states brought on by music only intensify as we grow. Happy music, usually featuring a fast tempo and written in a major key, can cause a person to breathe faster, a physical sign of happiness [source: Leutwyler]. Similarly, sad music, which tends to be in the minor keys and very slow, causes a slowing of the pulse and a rise in blood pressure. That seems to indicate that only happy music is beneficial, but those that know the value of a good cry or a cathartic release may find that sad or angry music can bring about happiness indirectly.
Knowing that music has this impact on the body may eventually influence treatment and care for a wealth of patients. For example, music has been found to boost the immune systems of patients after surgeries, lower stress in pregnant women and decrease the blood pressure and heart rate in cardiac patients, thus reducing complications from cardiac surgery [sources: Lloyd, Wiley-Blackwell]. Researchers at Cal State University found that hospitalized children were happier during music therapy, in which they could experiment with maracas and bells while a leader played the guitar, than during play therapy, when their options were toys and puzzles [source: Hendon and Bohon]. Music therapy has also proven to be more effective than other types of therapies in patients suffering from depression, and it's been shown to lower levels of anxiety and loneliness in the elderly [sources: Parker-Pope, Berger].
You don't have to be sick, though, to benefit from the reduced stress and increased happiness that music can bring. Live music may be the most potent happiness trigger because it provides a way to forge social bonds. When you get in a room with people who like the same thing you do, you might create more friendships, a proven factor in the search for happiness.
However, it's worth noting that too much music could be too much of a good thing. Since music triggers reward systems in our brains much like drugs do, music could also become an addiction that becomes impossible to feed. Having music around us constantly -- from department stores to elevators to our headphones -- could numb us to its effects. Unplugging that iPod every now and then might just help your favorite song sound sweeter later on.