Epidural injections are often used to treat radicular pain, also called sciatica , which is pain that radiates from the site of a pinched nerve in the low back to the area of the body aligned with that nerve, such as the back of the leg or into the foot. Inflammatory chemicals (. substance P, PLA2, arachidonic acid, TNF-α, IL-1, and prostaglandin E2) and immunologic mediators can generate pain and are associated with common back problems such as lumbar disc herniation or facet joint arthritis . These conditions, as well as many others, provoke inflammation that in turn can cause significant nerve root irritation and swelling.
Within the genitourinary and gastrointestinal tracts, commensal flora serve as biological barriers by competing with pathogenic bacteria for food and space and, in some cases, by changing the conditions in their environment, such as pH or available iron.  As a result of the symbiotic relationship between commensals and the immune system , the probability that pathogens will reach sufficient numbers to cause illness is reduced. However, since most antibiotics non-specifically target bacteria and do not affect fungi, oral antibiotics can lead to an "overgrowth" of fungi and cause conditions such as a vaginal candidiasis (a yeast infection).  There is good evidence that re-introduction of probiotic flora, such as pure cultures of the lactobacilli normally found in unpasteurized yogurt , helps restore a healthy balance of microbial populations in intestinal infections in children and encouraging preliminary data in studies on bacterial gastroenteritis , inflammatory bowel diseases , urinary tract infection and post-surgical infections .