Medical Daily: Study suggests that being too clean can make people sick: "Researchers also found that people age 18 and under with higher levels of triclosan were more likely to report diagnosis of allergies and hay fever."Triclosan is the common anti-bacterial agent in soap and other household products. While purporting to protect people from infection, these products a) don't actually work and b) often simply strengthen germs. And now we know that they actually harm health in the long run. Brilliant.
The article also notes that the chemical BPA can have similar negative effects on the immune system.