It's not surprising that we've had a big increase in allergies and the increase has been particularly so in Western countries like Britain, Canada, Australia and hasn't been seen as much in places like China, India and so on.

But I think one of the big changes have been changes in our environment. We've got a lot cleaner than we used to be. We've got houses that are more draft proofed, have got more I the way of soft furnishings. We are exposing our bodies to an increasing amount of chemicals in the environment that we live in. These are some of the chemicals in some of the products around our home some of the chemicals that we put in foods and some of the chemicals that we pump out into the atmosphere.

For example recently there was a paper about diesel particulates released from diesel engines that on their own don't do very much but combined with allergens can trigger off allergies in bodies.

It's probably that there's always been more than what we recognize it's just that we're getting better at recognizing some of it.