Studies in farmers' children have indicated that unpasteurised milk may protect against allergies and asthma. The reasons are unclear and these findings have not been confirmed in non-farmers. The current study will assess these protective effects in the general population, making use of a 'natural experiment'. It will involve 300 non-farming families who obtain raw milk through farmers with whom they have a 'cow-share agreement', which allows the provision of raw milk without contravening sales legislation. We will also recruit 150 families who do not consume unpasteurised milk. The study will assess whether raw milk is associated with a lower prevalence of allergies and asthma and improved lung function. It will also study the immunological mechanisms and the involvement of pathogenic bacteria. This study will contribute towards identifying the anti-allergic components within raw milk and has the potential to lead to novel and effective interventions for allergies and asthma.