What Causes Appendicitis?

Medically reviewed by Jay N. Yepuri, MD

Appendicitis is characterized by inflammation and infection of the appendix. The appendix is a finger-shaped, pouch-like organ in the lower right side of the abdomen. A blockage inside the appendix causes appendicitis.

There are two types of appendicitis: acute and chronic. Acute appendicitis occurs suddenly, with symptoms developing over 24-48 hours. Chronic appendicitis is long-term inflammation of the appendix. Symptoms are usually milder and come and go, lasting months or years.

Acute appendicitis is a medical emergency that requires prompt treatment. Without treatment, the appendix may rupture, spilling its contents (including infection) throughout the abdomen. About 1 in 15 people in the United States develop appendicitis in their lifetime.

Causes

Appendicitis develops when the opening of the appendix (lumen) becomes blocked. A blockage reduces blood flow to the organ, increases pressure, and traps bacteria inside the appendix, leading to appendicitis. There are several possible causes of appendix blockages, including constipation, swollen lymph nodes, and infections, among others.

Hard Stool and Constipation

A hardened mass of stool, or fecalith, can block the opening of the appendix. Constipation causes stool to move slowly through the digestive tract, where it can harden and become trapped, forming a hardened mass (fecalith). Once a fecalith forms, it can block the opening of the appendix. This can prevent stool and other fluids from exiting of the appendix, leading to inflammation and infection.

Swollen Lymph Nodes

Lymph nodes are small, bean-shaped glands that filter out bacteria, viruses, and other foreign substances from the body. An infection in the digestive tract or elsewhere in the body can cause swelling in the abdominal lymph nodes as they fight the infection. The enlarged lymph nodes can press on the appendix and block its opening, causing inflammation.

Bacterial, Viral, or Parasitic Infection

Sometimes bacterial, viral, or parasitic infections in the digestive tract or other abdominal organs can spread to the appendix. When this occurs, the infection in the appendix causes inflammation and swelling. Parasitic infections can block the opening of the appendix, preventing the flow of fluids and increasing the risk of appendix rupture.

Growths or Tumors

Benign growths, such as polyps, and malignant (cancerous) tumors in the appendix, large intestine, or ileocecum (where the small intestine meets the large intestine) can cause irritation or blockage in the appendix, leading to appendicitis.

Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), which includes ulcerative colitis and Crohn’s disease, causes chronic inflammation in the gastrointestinal tract. Inflammation associated with IBD can affect the appendix, increasing your risk of appendicitis. IBD can also cause the large intestine to narrow (stricture), blocking the flow of stool and fluids from the appendix and leading to appendicitis.

Trauma or Injury

Trauma or injury to the abdomen is a rare cause of appendicitis. It is possible for car accidents, sports injuries, and other physical traumas to damage the appendix. Sometimes, injury to the surrounding tissues can cause stool to become impacted in the appendix (fecalith) or lead to inflammation that blocks the appendiceal opening.

Foreign Bodies

Foreign bodies, such as fruit seeds or swallowed non-food items, can sometimes block the opening of the appendix. While most swallowed foreign bodies pass through the gastrointestinal tract without causing problems, in rare cases, a foreign body can enter the appendix and get stuck, causing inflammation and blockage that leads to appendicitis.

Chronic Appendicitis Causes

The causes of chronic appendicitis are not well understood. The leading theory suggests that chronic appendicitis develops due to a partial obstruction of the appendix. Some bacteria and stool can still get through when the appendix is partially obstructed. This may lead to ongoing and occasional inflammation and mild appendicitis symptoms.

In some cases, people with a history of mild acute appendicitis treated with antibiotics (rather than surgery) may develop chronic or recurrent appendicitis. 

Is Appendicitis Hereditary?

Appendicitis is not directly inherited, but there is some evidence that genetics may play a role in its development. Studies show that people with a family history of appendicitis are likelier to develop the condition.

Researchers have discovered variants in certain genes that are connected to an increased risk of appendicitis. These gene variants include:

• NEDD4L: NEDD4L is like a recipe in your cells that shows them how to make a special protein. This protein helps your cells communicate with each other as well as break down old proteins in your body. This variant may make the appendix more prone to inflammation and infection.

• IL-6: The IL-6 gene carries instructions for producing a protein that plays a role in your body's response to inflammation. Changes in this gene can increase your chances of getting appendicitis and experiencing more severe symptoms.

• IL-17: IL-17 is a gene that carries instructions for producing a protein involved in the immune response. Variations in the IL-17 gene are associated with a higher risk of appendicitis.

• HLX: HLX is a gene that carries instructions for producing a protein that is used for the development and maintenance of the appendix. Variations in the HLX gene may increase your risk of appendicitis.

• CTSB: CTSB is a gene that encodes a protein involved in cell death and the breakdown of proteins. Variations in the CTSB gene are linked to an increased risk of appendicitis and more severe symptoms.

Your risk of developing appendicitis is about three times higher if you have a first-degree relative (parent, sibling, or child) with a history of the condition.

Who Gets Appendicitis?

Anyone can get appendicitis, but some people are more likely to develop it than others. Several factors are associated with an increased risk of appendicitis, including:

• Age: Appendicitis is most common in children and young adults between 10 and 30.

• Sex: Appendicitis is slightly more common in people assigned male at birth than people assigned female at birth.

• Ethnicity: Rates of appendicitis are somewhat higher in Hispanics than in white or Black people.

• People who have had colorectal cancer: Colorectal cancer and appendicitis have an inverse relationship; people who have had one are more likely to develop the other.

• Children who had antibiotics in early life: Children who took antibiotics in the first 6 months of life are at an increased risk of developing appendicitis later on.

Risk Factors

Certain risk factors can increase your chances of developing appendicitis. Not everyone with these risk factors will develop appendicitis, and some people who develop appendicitis may not have any known risk factors.

Geography

Some studies suggest that socioeconomic status and where you live can affect your likelihood of developing appendicitis. A retrospective study that analyzed appendicitis-related hospitalizations in Washington state between 2008 and 2012 found that rates of appendicitis are higher in neighborhoods with lower median incomes.

A very large 2022 study found that warmer temperatures are associated with higher rates of appendicitis, which suggests people who live in warm climates may have a higher chance of developing appendicitis.

Diet

The foods you eat may influence your risk of appendicitis. A diet low in fiber and high in processed foods is associated with an increased risk of constipation and hard stools, which may lead to an appendix blockage. Research shows that eating a high-fiber diet with plenty of vegetables and fruits lowers the risk of appendicitis.

Smoking

Some research suggests a potential link between smoking and an increased risk of appendicitis. People who smoke have an increased risk of appendix perforation when the appendix bursts and spreads the infection throughout the abdomen. Smoking also constricts blood vessels, which may affect the blood supply to the appendix.

Related: What You Need to Know If You Want to Quit Smoking

Inflammatory Bowel Disease

People with inflammatory bowel disease (i.e. ulcerative colitis or Crohn's disease) are more likely to develop appendicitis. These conditions cause inflammation in the gastrointestinal tract, which can affect the appendix and lead to a blockage.

A Quick Review

Appendicitis is when the appendix—a small, pouch-like organ connected to the large intestine—becomes inflamed and infected. It is caused by a blockage inside the appendix, which restricts blood flow, traps bacteria, and increases pressure within the organ. Sources of appendix blockages include infections caused by bacteria, viruses, or parasites, hard, stone-like stools, swollen lymph nodes, and inflammatory bowel disease. 

Appendicitis can affect anyone, but it is most common in people between 10 and 30 years old. Certain factors can increase your risk of appendicitis, including being born male, eating a low-fiber diet, and having a family history of appendicitis. Appendicitis is a medical emergency that requires prompt treatment to prevent complications. 

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