Evidence is growing that dirt and germs protect against disease — and that our indoor-based, ultra-clean lifestyles are bad for our health. It is said that without exposure to dirt and germs early in life, the immune system doesn’t learn how to control its reaction to everyday invaders such as dust and pollen. This can lead to it mis-firing later in life, leading to allergies and other illnesses, the Daily Mail has reported. Taking course after course of antibiotics may exacerbate the problem. The latest evidence comes from Harvard Medical School researchers who studied germ-free mice, bred in a bubble and kept in sterile cages and fed sterile food. The lungs and bowels of the germ-free mice contained extra-large numbers of a type of immune cell blamed for asthma and bowel problems. And when they developed asthma or bowel condition colitis, it was much more severe than usual. Researchers looked at what happened when the rodents were taken out of their sterile environment and put in bug-ridden cages with normal mice. The mice that were moved as adults did not become any less susceptible to disease. But the germ-free creatures moved and exposed to dirt and bugs in the first weeks of life became no sicker than those reared normally, the journal Science reports