Appendicitis is a serious medical condition in which the appendix — a small, finger-shaped organ attached to your large intestine — becomes swollen and inflamed.

It's not always clear what causes appendicitis, but it's sometimes due to a viral, bacterial, or fungal infection that has spread to the appendix. Possible infections include, but are not limited to:

  • Bacteroides bacteria
  • Adenovirus
  • Salmonella bacteria
  • Shigella bacteria
  • Measles
  • The fungal infections mucormycosis and histoplasmosis

More often, appendicitis is the result of an obstruction of the area inside of the appendix, called the appendiceal lumen or appendix lumen. There are numerous issues that can cause appendix lumen blockage, including:

  • Appendicoliths or fecaliths, which are calcified fecal deposits, also known as "appendix stones"
  • Intestinal worms or parasites, including pinworm (Enterobius vermicularis)
  • Irritation and ulcers in the gastrointestinal (GI) tract resulting from long-lasting disorders, such as Crohn’s disease or ulcerative colitis
  • Abdominal injury or trauma
  • Enlarged lymph tissue of the wall of the appendix, which is typically the result of infections in the GI tract
  • Various foreign objects, such as stones, bullets, air gun pellets, and pins

Your appendix is home to many beneficial bacteria. However, when the organ becomes infected or blocked up, the bacteria multiply rapidly, causing your appendix to swell and fill with pus — a thick liquid containing bacteria, tissue cells, and dead, infection-fighting white blood cells.

Complications of Appendicitis

If left untreated, appendicitis will often get progressively worse as the inflammation leads to further complications.

Pressure within the appendix will increase, and this decreases the amount of blood flowing through the walls of the appendix, which then become starved of blood and start to die. Bacteria can leak out of the dying walls of the appendix, causing the peritoneum — the silk-like membrane that lines the abdominal cavity — to become infected.

Eventually, the appendix will rupture, spewing its contents throughout the abdomen. In some cases, abscesses (pockets of pus) may form on the ruptured appendix; if the abscesses tear, they can infect the rest of the abdomen.

In other cases, the ruptured appendix may cause the peritoneum to become infected, a condition called peritonitis. This serious complication can then lead to a potentially fatal blood infection called sepsis.

Appendicitis Risk Factors

There is no way to predict who will get appendicitis, but scientists have uncovered several risk factors for the condition. These include:

  • Having a family history of appendicitis
  • Being a male
  • Being between the ages of 10 and 19 years old
  • Having a long-lasting inflammatory bowel disease, such as Crohn’s disease or ulcerative colitis

Research also suggests that the typical "Western diet," which is high in carbohydrates and low in fiber, can increase your chances of developing appendicitis. Without enough fiber in your diet, bowel movements slow down, increasing the risk of appendix obstruction.

There is also a link between air pollution — in particular, high levels of ozone — and appendicitis. Scientists aren’t sure why air pollution is associated with an increased risk of appendicitis, but it may be that high levels of ozone increase intestinal inflammation or alter the normal communities of microbes in the gut.

Indeed, studies suggests that people get appendicitis more during the summer than other times of the year, likely due to a combination of increased air pollution, more GI infections, and greater consumption of fast food and other high-carb, low-fiber meals.