The Science of Rain and Happiness

From its distinctive scent to the negative ions it emits, rain brings some interesting benefits to our bodies, especially our mood.

The temperature had exceeded 38 degrees Celsius for the sixth consecutive day in New Milford, Connecticut, when the sky turned a terrifying dark red. I was leading an outdoor theater workshop, and I noticed that the camp participants were looking up at the long, ominous cloud that was approaching overhead. Then the thunder rumbled, shaking the ground, and lightning spread across the sky like a jagged web.

We heard the sound before we felt the water, and then we were suddenly drenched in a torrential downpour. No one could hear anyone else, so I gestured towards a nearby covered stage that had clothes bags, and my students and I, including myself, ran towards it. 

Soaked and laughing, we collapsed onto the pile of clothes and watched the storm rage outside. After about 30 minutes, the sky cleared, and the air felt surprisingly fresh and cool. The strong and distinctive scent of rain filled the surroundings.

When we returned to rehearsal, the grass and trees looked greener and healthier than ever. Everyone felt lighter, smiling easily, and I felt as if a burden had been lifted from my mind. Was it because the heatwave had ended, or because of the adrenaline rush from running for shelter, or did the rain have something to do with our collective mood improvement?

After decades of studying the elements that can improve mood, scientists have found some good evidence to support it. And this is not the only benefit of rain: research shows that rain removes harmful substances from the air, while its recognizable scent can even boost our memory.

• Increase in Serotonin 

The main reason for this may be that rain emits negative ions (oxygen molecules with extra electrons) into the air, which are formed when water droplets collide with each other or break upon hitting a surface. At high levels, these are known to increase serotonin and alpha waves in the brain, which put people in a happier and calmer state.

When raindrops hit the ground, they can splash and release negative ions into the air – a process called the 'Lenard effect'. So if you are hoping to get a large dose of negative ions to boost serotonin, try walking in the heavy rain. But for safety, stay indoors if you see lightning.

Some scientists believe that these positive effects may be due to negative ions increasing oxygen levels in the blood, resulting in mood improvement, similar to when one engages in strenuous exercise.

However, there is still no concrete evidence to explain exactly which mechanism is at work to produce these effects. According to Pam Dalton, a cognitive scientist at the Monell Chemical Senses Center in Pennsylvania, USA, how negative ions affect mood, as well as fatigue, cardiovascular condition, and blood pressure, is still not well understood. She says, 'While this is interesting, there is not much consensus on its physical benefits, and even less is understood about the potential mechanisms by which negative ions bring about these effects.'

The study of the effect of negative ions on mood began in the 1950s, although the results were inconclusive until the 1990s when high-voltage 'ionizers' that could produce negative ions more efficiently became available. In a notable study in 1995, researchers found that participants with seasonal affective disorder who were given daily sessions with high-voltage ionizers were more likely to experience a significant reduction in symptoms than those who received low-output treatment.

According to Professor Michael Terman of Columbia University, who led that study, heavy rain produces negative ions at a level similar to the high-voltage ionizer used by his team. But he also points out that no study has yet directly proven this, nor has it directly linked time spent in the rain to mood changes.

• Clean Air

Rain's negative ions also seem to make breathing easier by removing pollutants and allergy-causing particles from the air. This can also affect mood and health: since poor air quality is linked to increased anxiety and a higher risk of developing serious mental health disorders, it is logical to say that clean air does the opposite.

Dalton says, 'There is sufficient evidence that negative ions can remove dust, bacteria, allergens, and other particles from the air, which can have a positive effect on many people's respiratory health.' 

Until about a decade ago, it was not clear how adept negative ions were at cleaning the air. In a 2015 study, researchers replicated this ability on a small scale by pumping various types of particles into a glass chamber that generated water droplets.

After the water droplets evaporated, the researchers collected the remaining particles and noted their positions to determine if the water droplets had actually attracted them. They found that small water droplets were particularly adept at attracting these airborne particles.

Dan Cziko, an associate professor of Earth, Atmospheric, and Planetary Sciences at Purdue University in Indiana, USA, and co-author of the study, says, 'When raindrops fall to the ground, they essentially sweep away small particles of air in their path.' The electrical charge within the water droplet acts as a magnet for these particles, resulting in a 'sweeping' process known as 'coagulation'.

Cziko compares it to what happens when construction workers spray water in dusty areas; the airborne dust is pushed down to the ground, thereby cleaning the air.

The intensity of the rain also makes a difference. Cziko says, 'The heavier the rain, the more cleansing effect you will get in the atmosphere.' This includes reducing the amount of positive ions in the air, which are associated with irritability and increased anxiety.

So next time it rains heavily, consider opening your windows as soon as the rain stops. You will feel the air is cleaner, and if it comes behind a cold front (as heavy rain often does), the incoming wind can improve air quality by sending that clean air into your home.

• Memory-Boosting Scent

The distinctive scent of rain can also have a psychological effect. Known as 'petrichor', this smell rises from the ground after a storm and is often described as earthy and, in some ways, clean.

Professor Phil Stevenson, a professor of botanical chemistry at the University of Greenwich, who leads work on plant and fungal properties at Kew Gardens in the UK, says, 'Petrichor is produced when rain releases aerosols from the ground. In dry weather, organic molecules from plants, animals, and soil accumulate on surfaces. When water droplets hit, these molecules – including volatile plant oils – break into airborne particles.'

This clean scent is thought to be due to ozone, which can be pulled down to Earth by the winds of a storm after rain. Another part of this smell comes from geosmin, a chemical compound produced by 'actinomycete' bacteria in the soil when they form spores.

Stevenson says, 'Rain releases these spores and geosmin, creating the familiar 'first rain after drought' scent, which is most noticeable in warm weather.' 

This may explain why people are so sensitive to it – more so than sharks are to blood. Scientists speculate that we have evolved to understand that petrichor signifies a new abundance of fresh water, which perhaps helped our ancestors feel safe and calm.

These scents have been shown to cause distinct changes in alpha and beta wave activity in the brain associated with a calm and more relaxed state.

And thanks to its unique scent and the way it dramatically changes the environment, rain can also be a powerful trigger for nostalgia.

Dalton, who has studied the psychological significance of scents in detail, says, 'The scent of approaching rain or the experience after it can become a background or context that is linked to many of our different places or memories of feelings.'

She says, 'Any scent can activate the amygdala, the part of the brain that processes emotions and emotionally significant memories. Because of that connection to our emotional center, memories associated with scents tend to stick in the mind and remain vivid. So it doesn't matter whether you perceive the scent of rain as good or bad; what matters is the context in which you experience that scent makes it memorable.'

So next time it rains, take a deep breath through an open window or during a post-rain walk and see what details of long-past moments surface.

Comforting Sound

It's not just smelling and breathing in the scent of rain that makes us feel good; listening to its sound does the same, which is why you often find rain tracks on sound machines. Steady rain can reduce cortisol levels, which promotes a sense of calm and helps to mask disruptive noises.

Amy Sarow, a clinical audiologist working in outpatient care in Southfield, Michigan, USA, says, 'The sound of water is linked to the activation of the parasympathetic nervous system, a branch of the nervous system involved in rest and recovery. When this system is activated, we can see physiological effects such as a lower heart rate and a reduction in stress response.'

A recent study found that the sound of rain in the range of 40 to 50 decibels (equivalent to light, gentle rain) was most effective, reducing stress levels by up to 65%. Heavy rain, which falls at an even lower brown noise frequency, can feel even more profound and immersive, Sarow says, and can mask disruptive noises to promote sleep.

Both levels can be calming; Sarow says it often comes down to personal preference. She says, 'If a person intentionally listens to these sounds as part of a relaxation routine, that experience starts to resemble mindfulness or meditation practice, where the sound serves as a backdrop for focus and relaxation.'

Although my storm-rain experience didn't exactly put me in a meditative state, it made me feel better and more connected to the present moment. Now, every time it rains heavily, I try to spend a little more time immersing myself in it. 

Next time you see rain in the weather forecast, you might consider joining in this experience. You might be pleasantly surprised.

BBC