To live longer we should avoid smoking and fast food. But what if other people are slowly killing us? Dr Mhairi Bowe (Heriot-Watt University) wants to know the dangers posed by other folks – fear, aggression, discrimination and loneliness – and wonders if people might be the key that unlocks a long, happy life. She explores how psychology can explain why we like some people and can’t stand others, who’d help us if we fell over in the street, whose smelly shirt we are more disgusted by, and whose toothbrush you’d be happiest to share!