Sinus infections occur when certain types of bacteria infect the sinuses, causing nasal discharge, pressure and pain. Antibiotics are a way to treat sinus infections, but they are not without side effects. The same antibiotics that kill one kind of bacteria in the sinuses can also kill another kind of "good" bacteria in the intestines, leading to diarrhea.
Sinus infections result from bacterial infections that cause the tissues lining the sinus spaces to swell and become irritated. Strep and staph bacteria are most commonly associated with sinus infections, according to MayoClinic.com.
Bacteria in the intestines are considered "normal flora" and are not disease causing, or pathogenic. The bacteria help break down and process foods so that their nutrients can be absorbed. The flora, which include escherichia and lactobacillus species, also keep pathogenic bacteria at bay.
Since bacteria are everywhere in the environment, humans consume plenty of bacteria by accident from raw or undercooked food. Pathogenic bacteria include salmonella, shigella, clostridium and other species.
The type of antibiotics used in curing sinus infections also have an effect on good digestive bacteria. These antibiotics may not necessarily work on the bad intestinal bacteria. As the good die, the bad bacteria multiply and cause diarrhea, among other symptoms.
While most antibiotic-associated diarrhea cases clear up on their own as the good bacteria make a comeback, some people may need medical treatment with antibiotics that will also work on bad bacteria. The best treatment consists of both eliminating the bad bacteria and replacing the good bacteria. Yogurt, with its living cultures of lactobacillus, is a good food to help replace the good bacteria.