In a 2008 study, researchers took fecal samples from 35 babies when they were one week old. They measured the diversity of bacteria in those samples. When the babies were 18 months old, they were divided into two groups: with (n = 15) and without (n = 20) atopic dermatitis, commonly called a rash. Atopic dermatitis is a sign of an oversensitive immune system. Children with this problem are more likely to have allergy problems when they are older. The 2008 study found that the babies with atopic dermatitis had less diverse fecal bacteria.
This is more evidence connecting lack of bacteria with immune problems.