Core tip: An overly sanitized environment increases asthma and allergy risk. Some bacteria are good for boosting the body’s immune system, and without them, the body can become allergic to dust and pollen, leading to asthma. It is good for a person to love cleanliness, but focusing too much on cleanliness to the extent that it affects normal study, work and life, especially social interactions, belongs to cleanliness disorder. According to the latest foreign media reports, the British “molecular psychiatry” book published in the United States, a new study found that too clean will increase the incidence of depression. Scientists say, eliminate all bacteria and viruses will actually weaken the body’s immune system, which in turn will affect the brain function. Over-sanitized environments increase the risk of asthma and allergies. Some bacteria are good for boosting the body’s immune system, and without them, the body can develop allergies to dust and pollen, leading to asthma. Today scientists believe that too much cleanliness can also have a negative impact on the brain, affecting the brain’s production of euphoric chemicals such as serotonin, thus making it more likely to lead to depression. Scientists point out that the incidence of depression is higher in Western countries than in poorer countries because the human immune system is less exposed to “germs”. For example, the incidence of depression in the United Kingdom is 10 percent, while only 1 percent in Nigeria. Researchers in Atlanta, USA, studied the effects of allergic reactions or inflammation on the brain. The study involved 27 patients with hepatitis C who were being treated with medication. Hepatitis C can cause similar reactions. Scientists believe that certain reactions affect the brain’s production of “euphoria hormones”, including serotonin. Dr. Andrew Miller, the leader of the new study, said the body’s immune system improves as it grows and develops. Nowadays, environments are cleaner and more hygienic, and immune systems that have not been exposed to more germs are often overwhelmed by infectious agents (bacterial germs). The body’s immune system is better able to control inflammation if exposed to more bacteria or parasites. And immune system problems inevitably lead to an increased risk of depression.