Type 1 diabetes is a chronic condition in which the immune system attacks and destroys the cells in the pancreas that produce insulin. Without insulin, the body cannot move sugar from the bloodstream into cells for energy, causing blood sugar levels to rise dangerously high. About 9.5 million people worldwide are living with type 1 diabetes as of 2025, and roughly 513,000 new cases are diagnosed each year.
What Happens Inside the Body
Your pancreas contains clusters of cells called islets, and within those islets are beta cells, the only cells in your body that produce insulin. In type 1 diabetes, the immune system misidentifies these beta cells as threats and sends white blood cells to infiltrate the islets and destroy them. This process begins months or even years before any symptoms appear. During that silent window, the body produces detectable antibodies against its own beta cell proteins, a measurable sign that the immune attack is underway.
By the time symptoms show up, a significant portion of beta cell function has already been lost. The remaining cells can no longer produce enough insulin to keep blood sugar in a normal range. At that point, external insulin becomes a lifelong necessity. Unlike type 2 diabetes, where the body still makes insulin but doesn’t use it efficiently, type 1 involves an absolute shortage of insulin production.
Who Gets Type 1 Diabetes
Type 1 diabetes can develop at any age, though it’s most commonly diagnosed in children and young adults. Of the 9.5 million people living with the condition globally, about 1 million are under 15 and another 800,000 are between 15 and 19. Incidence is rising by about 2.4% per year, with the sharpest increases in lower-income countries, where the number of people with type 1 diabetes grew 20% between 2021 and 2025.
Genetics play a role. Certain gene variants related to the immune system make some people more susceptible. But having those genes doesn’t guarantee you’ll develop the disease, and most people diagnosed have no family history of it. Environmental triggers, possibly viral infections or other factors early in life, are thought to set the autoimmune process in motion in genetically predisposed individuals.
Symptoms and Warning Signs
The classic early symptoms are intense thirst and frequent urination. When blood sugar runs high, your kidneys work overtime to filter the excess glucose, pulling water with it. This leads to dehydration, which makes you thirstier. You may also notice unexplained weight loss, because without insulin your body starts breaking down fat and muscle for energy instead of using glucose. Extreme fatigue and blurred vision are common too.
If blood sugar stays high without treatment, the body begins breaking down fat so rapidly that it produces acids called ketones. This leads to a dangerous condition called diabetic ketoacidosis, or DKA. Signs of DKA include fast, deep breathing, fruity-smelling breath, nausea and vomiting, stomach pain, and dry skin. DKA is a medical emergency. In many cases, it’s actually the event that leads to an initial type 1 diagnosis, because the person didn’t know their blood sugar had been climbing.
How Type 1 Diabetes Is Diagnosed
Diagnosis relies on blood sugar measurements. Diabetes is confirmed when fasting blood glucose reaches 126 mg/dL or higher, a two-hour glucose tolerance test hits 200 mg/dL or above, or an A1C test (which reflects average blood sugar over two to three months) comes in at 6.5% or greater.
To distinguish type 1 from type 2, doctors test for autoantibodies, immune proteins that target beta cell components. There are four main ones, directed against insulin, two enzyme proteins found in beta cells, and a zinc transporter on the beta cell surface. At least one of these autoantibodies shows up in 93% to 96% of people with type 1 diabetes. Their presence confirms the autoimmune nature of the disease and rules out type 2, which matters because treatment is fundamentally different.
Living With Insulin
Everyone with type 1 diabetes needs external insulin, either through injections or an insulin pump. The goal is to mimic what a healthy pancreas does naturally: provide a steady background level of insulin throughout the day and release quick bursts at mealtimes.
Long-acting insulin handles the background. It starts working about two hours after injection, doesn’t spike, and lasts up to 24 hours. You typically take it once or twice a day. Rapid-acting insulin covers meals. It kicks in within 15 minutes, peaks at about one hour, and wears off in two to four hours. You take it right before eating, matched to the amount of carbohydrates in your meal. There’s also an inhaled rapid-acting form that starts working in 10 to 15 minutes and lasts about three hours.
Getting the balance right requires constant attention. Too much insulin drops blood sugar too low (hypoglycemia), and too little lets it run too high (hyperglycemia). Both are problems, but hypoglycemia is the more immediate danger.
Managing Low Blood Sugar
Blood sugar below 70 mg/dL is considered low. Symptoms include shakiness, sweating, confusion, irritability, and a racing heartbeat. If you feel these, the standard approach is the 15-15 rule: eat or drink 15 grams of fast-acting carbohydrates (four glucose tablets, half a cup of juice, or a tablespoon of honey), wait 15 minutes, then recheck your blood sugar. If it’s still under 70, repeat. Once it’s back in range, follow up with a balanced snack or meal that includes protein to keep it stable.
Severe hypoglycemia, where blood sugar drops so low you can’t treat yourself, requires help from someone else, usually through an emergency injection of a hormone that signals the liver to release stored glucose.
Monitoring With Technology
Most people with type 1 diabetes now use a continuous glucose monitor, or CGM. It’s a small sensor, typically worn on the arm or abdomen, that reads glucose levels every few minutes and sends the data to your phone or a receiver. This replaces most finger-prick testing and gives you a real-time picture of where your blood sugar is headed, not just where it is right now.
A key metric from CGM data is “time in range,” the percentage of the day your glucose stays between 70 and 180 mg/dL. The goal for most adults with type 1 is to spend at least 70% of the day in that range. Hitting that target is associated with fewer complications over time. Many people pair a CGM with an insulin pump in what’s sometimes called a hybrid closed-loop system, where the pump automatically adjusts background insulin delivery based on CGM readings.
Long-Term Complications
Chronically elevated blood sugar damages blood vessels over years. The mechanism involves excess glucose triggering oxidative stress and the buildup of harmful compounds that stiffen and narrow vessels, reducing blood flow and making vessel walls more permeable. This affects both small and large blood vessels throughout the body.
About half of people with diabetes develop complications involving small blood vessels. The three most common are damage to the retina (which is the leading cause of new blindness in developed countries), kidney disease (which can progress to kidney failure requiring dialysis or transplant), and nerve damage, particularly in the feet and legs, which impairs sensation and can ultimately lead to amputation. Organs with heavy blood flow, like the kidneys, are especially vulnerable.
Large blood vessel complications include heart disease, stroke, and peripheral artery disease. The good news is that keeping blood sugar closer to normal dramatically reduces the risk of all these complications. That’s the core reason behind the daily work of insulin dosing, carb counting, and glucose monitoring.
Treatments That May Delay Onset
For people identified as high-risk through autoantibody testing but not yet showing symptoms, there is now a treatment option that can delay the disease. An immunotherapy drug called teplizumab, given as a 14-day intravenous course, interferes with the immune cells that attack beta cells. In clinical trials, 72% of people receiving a placebo progressed to clinical diabetes within about two years, compared to 43% of those who received the drug. Among those in the treatment group who did eventually develop diabetes, diagnosis was delayed by a median of four years instead of two. It doesn’t prevent type 1 diabetes, but buying additional years of full pancreatic function is meaningful, especially for children.