Happiness derived from tasks that help others, like raising money for a charity, could be better for teen mental health than happiness derived from selfish activities, like eating chocolate or listening to music, according to research by Adriana Galvan of the University of California and her colleagues. Galvan and her team studied how teens' brains respond to these two different ways of finding happiness. They found that teens who are more likely to gain pleasure from helpful tasks are less likely to develop depressive symptoms than teens who are more likely to gain pleasure from selfish ones. The study appears in the Proceedings of the National Academy of Sciences.

As far back as the fourth century BC, Aristotle argued that pleasure gained from a meaningful life, which he called "eudaimonia," promoted human growth, while selfish pleasure, which he called "hedonia," was detrimental to it. More recently, empirical psychological studies have indicated that, over time, eudaimoniac activities tend to be beneficial to mental health while hedonic activities can be harmful to it.

http://medicalxpress.com/news/2014-04-teens-gain-pleasure-prone-depression.html