Archaeological evidence suggests that parents have used lullabies to soothe their young for at least 4,000 years [source: Perry]. Despite the general assumption that lullabies help babies relax, it wasn't until fairly recently that scientists began to understand exactly why these gentle tunes are so effective.
One simple explanation is that lullabies feature a triple meter, or 6/8 time. This gives the song a rocking or swaying rhythm, closely matching the movements the fetus experienced while in the womb. By recreating this womb experience through song, parents can comfort a child and soothe him or her off to sleep [source: Perry].
However, modern research methods have found that lullabies do much more than help Baby sleep. These songs actually create a physiological response in the body, which can have far-reaching effects on health and wellness.
In a 2010 study, researchers played recorded lullabies to premature infants in the intensive care unit of a hospital. These recorded tracks improved oxygen levels and respiration rates but failed to affect other areas, like heart rate and weight gain [source: Farhat et al].
When another group of scientists repeated this experiment in 2013 using live music, they found the lullabies had an even greater effect. The premature infants enjoyed improved respiratory function, reduced heart rates — indicating lower stress levels — as well as better sleeping and sucking patterns. Even more surprising is that singing these lullabies actually reduced parental stress as well [source: Loewy et al].
While it could be argued that simply speaking to a baby would have the same effect as singing, a 1997 Brigham Young University study showed this isn't necessarily the case. A group of preemies who listened to recorded singing enjoyed greater health benefits than those who listened to a recording of spoken words or those who listened to no recording to all [source: Michele et al]. The babies who listened to lullabies showed such improvement that they were able to leave the hospital an average of three days sooner than the other babies in the experiment. Researchers believe that they benefited from the smooth, even rhythm of the tunes [source: Walker].
A 2013 study in the United Kingdom found that listening to lullabies during a medical procedure actually reduced stress and pain levels [source: Great Ormond Street Hospital for Children]. In the study, lullabies were more effective than spoken stories at reducing stress and pain for children. It's possible that these songs activate the brain's limbic system, which responds to the melodies by releasing pain-killing endorphins [source: Penn State].