A new study suggests that early exposureto germs strengthens the immune system.That means letting children get a little dirtymight be good for their health later in life.The study involved laboratory mice.It found that adult mice raisedin a germ-free environmentwere more likely to develop allergies,asthma and other autoimmune disorders.There are more than eighty disorderswhere cells that normally defend the bodyinstead attack tissues and organs.They include rheumatoid arthritis,which attacks the joints; Crohn's disease,an inflammatory bowel condition;and juvenile diabetes. Hay fever, a common allergy,is also an autoimmune disorder.APRichard Blumberg is a professorat Harvard Medical School in Boston, Massachusetts.He says in nineteen eighty-nine,medical researchers sought to explain these diseaseswith what they called the "hygiene hypothesis."They proposed that the increasing use ofantibacterial soaps and other products,especially early in life, could weaken immune systems.RICHARD BLUMBERG: "The hypothesis has statedor suggested that early-life exposure to microbesis a very important determinant of later life sensitivityto allergic and so-called autoimmune diseases,such as hay fever, asthma,inflammatory bowel disease and others."Now, Dr. Blumberg and a team have what they sayis the first biological evidence to link early exposureto germs to stronger adult immune systems.They say this exposure could preventthe development of some autoimmune diseases.In the adult germ-free mice,they found that inflammation in the lungs and colonwas caused by so-called killer T cells.These normally fight infection.But they became overactive and targeted healthy tissue-- an autoimmune condition seen in asthmaand a disease called ulcerative colitis.Dr. Blumberg says the mice raised in a normal environmentdid not have the same reaction.He says their immune systems had been "educated"by early exposure to germs.Rates of autoimmune disorders are rising worldwide,but mostly in wealthier, industrialized countries.RICHARD BLUMBERG: "I think one obvious question,for example, that's raised by these studiesis the early life use of antibiotics and whether we needto be more careful in their prescribing."Rob Dunn is a professor of ecology and evolutionary biologyat North Carolina State University in Raleigh.He says the new study does not mean people should stop washing.ROB DUNN: "Wash your hands,but don't do it with antimicrobial soap.Let your kids play in a reasonable amount of dirtand get outside and get exposed to a diversity of things."The study appears in the journal Science.And that's the VOA Special English Health Report.