Modern lifestyles create an environment that tends to cause intestinal deterioration.
While age causes changes in the balance of intestinal bacteria, there are other factors that we can control that also affect it. Alcohol, stress, and an unbalanced diet reduce the number of good bacteria and increase the number of bad bacteria. Even young people can develop an intestinal environment that is close to that of an elderly person as a result of an unbalanced diet and stress. People who have a cold or a mouth ulcer have reduced Bifidobacteria and increased E. coli and Enterococcus. The same tendency is seen when people are constipated or have diarrhea.
Furthermore, taking antibiotics reduces intestinal bacteria, and if you do not have a well-balanced diet at that time, your intestinal flora balance may shift to having more bad than good bacteria.
It is now known that antibiotics, steroid hormones, immunosuppressive drugs, and radiation therapy increase pathogenic bacteria.