‘Healthy mood spreads through social contact, depression doesn’t’, http://www.medicalnewstoday.com/releases/298321.php, Medical News Today (19 August 2015).

Friends

While depression does not ‘spread’, having enough friends with healthy mood can halve the probability of developing, or double the probability of recovering from, depression over a 6-12 month period. (…) Results suggest that promotion of any friendship between adolescents can reduce depression since having depressed friends does not put them at risk, but having healthy friends is both protective and curative.