It is interesting to note that covering body with mud or lying in mud on beaches is not an act of getting dirty but it is an important way to improve mood & feel relaxed. Bacteria found in the soil activates a group of neurons that produce the brain chemical SEROTONIN which affects mood of a person.
A treatment was done on a mice with a friendly bacteria normally found in the soil this altered the behavior of mice in a way similar to that produced by antidepressant drugs according to a research report published in the latest issue of Neuroscience.
The scientist treated the brains of mice with Mycobacterium vaccae and found that this bacteria activated a group of neurons that produce the brain chemical serotonin. Lack of Serotonin causes depression in people. Therefore alteration in the behavior of mice was due to release of Serotonin in parts of the brain by the bacteria Mycobacterium vaccae.