In 1958, British physician David P Strachan, began a twenty-three year study on individuals from birth to twenty-three years of age which was published in the 1989 edition of the British Medical Journal in an article titled, "Hey fever, hygiene, and household size". In this study, Strachan compared the auto immune and allergic disease rates between over 17,000 children growing up in different levels of cleanliness in the United Kingdom. By the end of his twenty-three year study, Strachan determined that a decline in family size and an increase in cleanliness within the average British household had a direct relationship with the growing number of children and young adults who presented with hay fever, asthma, and eczema, and thus, hygiene hypothesis was born (8). In more recent years, some scientists have even proposed a correlation between hygiene hypothesis and many other autoimmune diseases, including lupus, type one diabetes, and even cancer.
In order to understand hygiene hypothesis, the human immune system must be discussed. Every living organism is at risk of disease and infection, and it is up to that organism's immune system to protect it from disease. Mammals, particularly humans, are among the species with the most complex and adaptive immune systems. In the third edition of, "Microbiology - A Systems Approach (third ed.)", microbiologist, Marjorie Kelly Cowan, describes the phases of infection and the inner workings of the human immune system. According to Cowan, an infection begins as soon as a foreign organism enters the body, and subsequently, the immune system is activated immediately (2). Once the immune system is activated, a cascading chain of events will create an immunity to the invading infection. As Cowan explains, cell bodies called lymphocytes (better known as white blood cells) will first, recognize a pathogen and send signals out to other lymphocytes to aid in the destruction of the pathogen.
