‘Noble deeds and hot baths are the best cures for depression,’ wrote author Dodie Smith in I Capture The Castle. ‘I am sure there are things that can’t be cured by a good bath but I can’t think of one,’ Sylvia Plath agreed in The Bell Jar. A long, hot soak has long been seen as the remedy for many of life’s challenges – and now a new study has proved that the theory may actually have a grounding in science.