Everybody can appreciate acts of kindness. But when it comes to explaining why we do them, people often take one of two extreme positions.
Some think kindness is something completely selfless that we do out of love and care, while others believe it is just a tool that we cunningly use to become more popular and reap the benefits.
But research shows that being kind to others can actually make us genuinely happy in a number of different ways. We know that deciding to be generous or cooperating with others activates an area of the brain called the striatum.
Interestingly, this area responds to things we find rewarding, such as nice food and even addictive drugs. The feel-good emotion from helping has been termed "warm glow" and the activity we see in the striatum is the likely biological basis of that feeling.
Of course, you don't have to scan brains to see that kindness has this kind of benefit. Research in psychology shows a link between kindness and well-being throughout life, starting at a very young age.
In fact, even just reflecting on having been kind in the past may be enough to improve teenagers' mood. Research has also shown that spending extra money on other people may be more powerful in increasing happiness than spending it on yourself.
But why and how does kindness make us so happy? There are a number of different mechanisms involved, and how powerful they are in making us feel good may depend on our personalities.
1. Contagious smiling
Being kind is likely to make someone smile and if you see that smile for yourself, it might be catchy.
A key theory about how we understand other people in neuroscience suggests that seeing someone else show an emotion automatically activates the same areas of the brain as if we experienced that emotion for ourselves.
You may have been in a situation where you find yourself laughing just because someone else is – why not set off that chain of good feelings with a nice surprise for someone?
2. Righting a wrong
The same mechanism also makes us empathise with others when they are feeling negative, which could make us feel down.
This is particularly true for close friends and family, as our representations of them in the brain physically overlap with our representations of ourselves.
Doing a kind act to make someone who is sad feel better can also make us feel good – partly because we feel the same relief they do and partly because we are putting something right.
Although this effect is especially powerful for people we are close to, it can even apply to humanitarian problems such as poverty or climate change.
Getting engaged with charities that tackle these issues provide a way to have a positive impact, which in turn improves mood.
3. Making connections
Being kind opens up many different possibilities to start or develop a social connection with someone. Kind acts such as a buying someone a thoughtful present or even just a coffee strengthens friendships, and that in itself is linked to improved mood.
Similarly, charities offer the opportunity to connect with someone on the other side of the world through donating to improve their life. Volunteering also opens up new circles of people to connect with, both other volunteers and those you are helping.
4. A kind identity
Most people would like to think of themselves as a kind person, so acts of kindness help us to demonstrate that positive identity and make us feel proud of ourselves.
In one recent study, even children in their first year of secondary school recognised how being kind can make you feel "better as a person … more complete", leading to feelings of happiness.
This effect is even more powerful when the kind act links with other aspects of our personality, perhaps creating a more purposeful feeling.
For example, an animal-lover could rescue a bird, an art-lover could donate to a gallery or a retired teacher could volunteer at an after-school group. Research suggests that the more someone identifies with the organisation they volunteer for, the more satisfied they are.
5. Kindness comes back around
Work on the psychology of kindness shows that one out of several possible motivations is reciprocity, the returning of a favour. This can happen directly or indirectly.
Someone might remember that you helped them out last time and therefore be more likely to help you in the future. It could also be that one person being kind makes others in the group more kind, which lifts everyone's spirits.
Imagine that you bake cakes for the office and it catches on so someone does it each month. That is a lot more days that you're getting cakes than providing them.
The story doesn't end there. Being kind may boost your mood, but research has also shown that being in a good mood can make you more kind. This makes it a wonderful two-way relationship which just keeps giving.