Multiple sclerosis, a disease where the fatty insulation around the nervous system comes under attack, appears to be on the rise, and type I diabetes, "a childhood form of diabetes almost unheard of at the turn of the 20th century, is up from one in 5,000 or 10,000 to one in 250 in some regions," said Joel Weinstock, chief of gastroenterology at Tufts University Medical Center in Massachusetts.
Even hay fever, which plagues roughly 1 out of 4 people in the United States, is something that may have largely emerged only in the 20th century, Weinstock said "What if I told you that there are some countries that don't even know what hay fever is?" he asked.
The rise of these disorders might be due to the very improvements in hygiene that have helped reduce infections in much of the world. The body's immune system is regularly exposed to antigens, molecules that it recognizes and reacts to, such as compounds from viruses or bacteria.
"But the immune system needs to be controlled, needs to not act up when exposed to things that aren't truly injuring you," Weinstock explained. "What we think is happening is the regulation mechanisms are becoming less effective. As to why that is, is it possible that it's due to lack of exposure to antigens? Do you need to be exposed regularly to antigens for it to work properly?"