The new slogan for Persil is revolutionary. Traditionally, the home-care giants have invoked fear, uncertainty and doubt in the shape of germs, viruses and other invisible horrors. When they weren't doing that, they tapped the neuroses of the desperate housewife. So Domestos kills all known germs, while Persil washes whiter. But Persil has changed its mind. In the TV and cinema ads created by JWT, a nice lady tells us: 'We see dirt differently. We believe dirt is good.' The global slogan meets two needs, one rational, the other emotional. Medical science tells us children need early exposure to germs if their immune systems are to develop. And most of us remember our mums saying: 'It's only a bit of dirt. It'll soon wash off.' It will with Persil. Science stays off the screen, as do white coats, washing machines and impressionable ladies hugging boxes of detergent. Instead, we get idealised, sentimental domestic scenes, reminding us why we love our children and our elderly parents, no matter how grubby they get. Dirt is good, but love is better.