You have one appendix. It’s a small, finger-shaped pouch attached to the beginning of your large intestine, on the lower right side of your abdomen. While the word “appendix” might sound like something that comes in multiples, every human is born with just one.
Where Your Appendix Sits
The appendix connects to the cecum, which is the first section of your large intestine, right where the small intestine joins it. It’s a narrow tube, typically about 5 millimeters wide, with walls less than 2.5 millimeters thick. In length, it ranges from about 2 to 4 inches in most adults, though it can occasionally be longer. Its position in the lower right abdomen is why appendicitis pain typically starts near the belly button and then shifts to that side.
Can You Have More Than One?
In extremely rare cases, yes. A condition called appendix duplication occurs in roughly 1 in 25,000 people. Since it was first classified in 1936, only about 100 cases have ever been reported in the medical literature. So while it’s technically possible to be born with two, it’s so uncommon that most surgeons will never encounter it in their careers. The vast majority of people have exactly one.
What Your Appendix Actually Does
For over a century, the appendix was dismissed as a useless leftover from evolution. That view has changed significantly. Your appendix serves two roles that scientists now consider genuinely useful.
First, it acts as a reservoir for beneficial gut bacteria. Think of it as a safe house. When an illness like food poisoning or a severe stomach bug wipes out the bacterial population in your intestines, the appendix can resupply your gut with healthy microbes to help it recover. The appendix’s narrow shape and dead-end structure protect these bacteria from being flushed out during bouts of diarrhea.
Second, it’s packed with immune cells, particularly B cells and T cells. These cells help your body learn to distinguish harmless bacteria from dangerous ones. This immune training function is especially important during childhood, when the immune system is still developing.
What Happens If It’s Removed
Despite its useful roles, your body adapts well without an appendix. People who have had an appendectomy eat the same foods, enjoy the same activities, and live without any functional limitations. The rest of your immune system and gut compensate for the loss.
Appendectomy is one of the most common emergency surgeries performed worldwide. The lifetime risk of needing one is about 8.6% for men and 6.7% for women, and rates have actually been declining over the past 30 years in the United States and Europe. Most people recover from the surgery within a few weeks and notice no lasting changes to their digestion or overall health.
Why Appendicitis Happens
Appendicitis occurs when the opening of the appendix gets blocked, usually by hardened stool, mucus, or swollen lymph tissue. Bacteria then multiply inside the sealed-off pouch, causing swelling, pain, and infection. The classic warning signs are pain that starts around your belly button and migrates to the lower right abdomen, nausea, fever, and loss of appetite. Left untreated, an inflamed appendix can rupture, which spreads infection into the abdominal cavity and becomes a serious medical emergency.
Appendicitis peaks between the ages of 10 and 30 but can happen at any age. There’s no reliable way to prevent it, and no diet or lifestyle change that eliminates the risk. The good news is that it’s highly treatable when caught early.