Are we sparing the dirt and spoiling our children's immune systems? The theory that some germs are necessary in developing healthy immune systems is gaining credence.

Are we sparing the dirt and spoiling our children's immune systems? The theory that some germs are necessary in developing healthy immune systems is gaining credence.

Allergic disorders (asthma, hayfever, eczema) now afflict as many as 40 per cent of all children in some European or American inner cities. Numerous groups have looked closely at the epidemiology of allergies. Their findings are compatible with the view that the crucial factor is diminished exposure to micro-organisms due to increased hygiene and antibiotic use. Moreover, there is a simultaneous increase in unwanted immune responses to things that the immune system should ignore. More people have immune systems attacking their gut contents (Crohn's disease) or their own tissues (multiple sclerosis). The link is faulty regulation of the immune system.

Mammals evolved in mud, and humans evolved close to earth and untreated water. Some organisms that are very common in mud and untreated water, such as mycobacteria, are rare on concrete or in chlorinated water. Moreover, there is proof that exposure to mycobacteria has been hugely reduced in Western countries.

It is vital that we find out which germs are needed, when and how, before the increase in diseases attributable to faulty regulation of the immune system spirals out of control.