The Psychologicalal and Physiological Benefits of Nature Therapy There is a commonly held belief in the world of psychology that a majority of mental health problems, up to 90 % if not more, are directly caused by stress (Jeffrey 2020). This includes prevalent conditions such as depression, anxiety, OCD, and social phobia, among others. Furthermore it is widely accepted that the five main factors that exert a positive influence on people’s mental health are a good night’s sleep, a healthy diet, regular exercise, access to fresh air, and exposure to sunlight. A sixth factor which is considered to be of significant importance is meaningful connections (Jeffrey 2020). While the value of the first five factors given above has been instinctively understood by mental health professionals for a long time, reasonably recent advances in the scientific disciplines of neurology and physiology have been able to provide quantifiable explanations for the processes and mechanisms involved. The concept of Nature Therapy or Forest therapy makes use of four of the first five factors listed above to try to achieve improvements in the mental health of participants. The various processes involved in these improvements are detailed here, and their therapeutic potential for the treatment of mental health problems are examined. As far back as 1982 the Japanese government sponsored and promoted what is referred to in Japan as Shinrin-yoku, or forest bathing (Livni 2016). It involves providing opportunity to people experiencing significant stress in their daily lives to spend time in natural environments, based on the underlying notion that exposure to these environments is beneficial to mental health in a variety of ways, including alleviating stress. Featuring prominently in such experiences is extended close proximity to natural vegetation, specifically trees, and running water, such as found in waterfalls, near rivers or on beaches. Combined with the exposure to direct sunlight (MHA 2017), these experiences have been found to have positive effects on people’s mental health for the reasons detailed below. 1. Sunlight It has been found that direct exposure to sunlight, particularly in the early hours of the morning, does two main things. Firstly, when sunlight enters the human eye it activates the retinal ganglion cells, a type of neurons situated near the inner surfcace of the retina of the eye. This causes an increase in the amount and the rate of production of the hormone serotonin, which regulates mood and emotions, and is commonly associated with wellbeing and happiness. Studies have found that a lack of serotoin is a major contributor to depression (Mead 2008). Secondly exposure to direct sunlight, at those early hours of the morning, oppresses and regulates the production of the hormone melatonin, the hormone that induces sleepiness, until the sun goes down at night. Sufficient exposure to sunlight keeps the hormone dormant during the daytime, and allows for its activation at night, when it is needed. This promotes the synchronisation of the body clock to a light-dark cycle, which results in improved mental