The benefits of outdoor swimming or cold baths have long been documented by scientists.
Now a group of south coast researchers have shown what happens in the brain when people take the plunge.
The team conducted MRI scans on volunteers before and after they went in cold water.
By comparing the results, they were able to see changes in the parts of the brain that control our feelings and levels of alertness.
It also showed how the brain adapts to help people get over the initial shock of the cold.
The study was led by Dr Ala Yankouskaya, Senior Lecturer in Psychology at Bournemouth University, and also involved Portsmouth University and University Hospitals Dorset.
Dr Yankouskaya said: "After our participants went in the cold water, we saw the physiological effects – such as shivering and heavy breathing. The MRI scans then showed us how the brain rewires its connectivity to help the person cope with the shock."
She continued: "When the participants told us that they felt more alert, excited and generally better after their cold bath, we expected to see changes to the connectivity between the medial prefrontal cortex and the parietal cortex (which control emotions, decision making and alertness). And that is exactly what we found."
They team is now planning to find out more about how depression and anxiety affect connections in the brain.