Type 1 diabetes is a chronic autoimmune condition in which the body’s immune system destroys the cells in the pancreas that produce insulin. Without insulin, glucose builds up in the bloodstream instead of entering cells for energy. About 1.9 million children and young adults worldwide live with type 1 diabetes, and more than 200,000 new cases are diagnosed in people under 20 each year.
What Happens in the Body
Your pancreas contains clusters of cells called islets, and within those islets are beta cells, which are the only cells that make insulin. In type 1 diabetes, specific immune cells mistakenly identify beta cells as foreign invaders and attack them. One type of immune cell makes direct contact with beta cells and kills them using toxic proteins. Another type releases inflammatory signals that poison beta cells and recruit even more immune cells to the area, creating a cycle of destruction.
This process typically unfolds over months or years before symptoms appear. By the time most people are diagnosed, a large percentage of their beta cells are already gone. Once destroyed, beta cells don’t regenerate, which is why type 1 diabetes requires lifelong insulin replacement.
How It Differs From Type 2 Diabetes
The core problem in type 1 is that the body stops making insulin entirely. In type 2, the body still produces insulin but cells become resistant to it, and insulin production may gradually decline over time. Type 1 can develop at any age but most commonly appears in childhood and adolescence, with peak incidence around age 10. Type 2 is more strongly linked to weight, physical activity, and aging, though it increasingly appears in younger people as well.
People with type 1 diabetes always need external insulin to survive. Many people with type 2 can initially manage their condition through diet, exercise, and non-insulin medications, though some eventually need insulin too. The two conditions share the outcome of high blood sugar but arrive there through fundamentally different paths.
Causes and Risk Factors
Both genetics and environment play a role, though the exact triggers remain unclear. The strongest genetic link involves a set of immune-related genes. People who inherit two specific gene variants (known as DR3 and DR4) from each parent have roughly 16 times the risk of developing type 1 compared to the general population. Inheriting just one of these variants still raises risk about five to sixfold. On the other hand, some gene variants are strongly protective, reducing risk to near zero.
Genetics alone don’t explain who gets type 1 diabetes. Most people with high-risk genes never develop it, and some people with low-risk genes do. Environmental factors, possibly viral infections or other immune triggers early in life, appear to set the autoimmune process in motion in genetically susceptible individuals. Rates have been climbing steadily: in U.S. youth, incidence rose about 2% per year between 2002 and 2018, a pace too fast to be explained by genetics alone.
Symptoms and Warning Signs
The early symptoms of type 1 diabetes often come on over a few weeks and are easy to overlook or attribute to something else. Extreme thirst and frequent urination are usually the first to appear, driven by excess glucose pulling water into the urine. Unexplained weight loss, constant hunger, fatigue, and blurred vision are also common.
If undiagnosed or untreated, type 1 diabetes can progress to a dangerous condition called diabetic ketoacidosis (DKA). Without insulin, the body breaks down fat for energy and produces acidic byproducts called ketones. DKA symptoms include nausea and vomiting, stomach pain, rapid deep breathing, fruity-smelling breath, and extreme fatigue. Blood sugar levels above 300 mg/dL combined with these symptoms require emergency care. DKA is the first sign of type 1 diabetes in a significant number of newly diagnosed cases, particularly in young children.
Who Gets Type 1 Diabetes
Type 1 diabetes is often called a childhood disease, but adults develop it too. In U.S. youth, the highest incidence is in children ages 10 to 14, at about 33 per 100,000 per year. Boys tend to peak slightly later (around age 12) than girls (around age 10). But data from a large California healthcare system found that adults ages 20 to 45 were diagnosed at a rate of about 30 per 100,000 per year, comparable to the childhood peak. Men are diagnosed slightly more often than women in adulthood.
Adults with type 1 are sometimes initially misdiagnosed with type 2 because of their age. Blood tests for diabetes-related antibodies can confirm the autoimmune nature of the condition.
How Type 1 Diabetes Is Managed
Everyone with type 1 diabetes needs to replace the insulin their body no longer makes. This is done through multiple daily injections or an insulin pump that delivers small, continuous doses through a tiny tube under the skin. The goal is to keep blood sugar within a target range, mimicking what a healthy pancreas would do automatically.
Continuous glucose monitors (CGMs) have transformed daily management. These small sensors, worn on the skin, measure glucose levels every few minutes and send readings to a phone or receiver. They alert you when levels are trending too high or too low, often before you feel symptoms.
The most advanced current technology pairs a CGM with an insulin pump in what’s called a hybrid closed-loop system. A computer algorithm reads your glucose data and automatically adjusts your background insulin dose throughout the day and night. It can increase insulin when glucose is rising and reduce or suspend delivery when levels are dropping. These systems are called “hybrid” because you still need to manually enter insulin doses at mealtimes. They significantly reduce the time spent with both high and low blood sugar, and they’re especially helpful overnight when you can’t actively monitor yourself.
Some systems go further. Predictive low-glucose suspend technology can detect a drop in blood sugar up to 30 minutes before it happens and pause insulin delivery preemptively. Fully closed-loop systems, which aim to handle even mealtime dosing automatically, are in active development. There are also do-it-yourself systems built by the diabetes community using open-source software connected to commercial pumps and sensors.
Low Blood Sugar Emergencies
Hypoglycemia, or low blood sugar, is the most immediate day-to-day risk of insulin therapy. Mild episodes cause shakiness, sweating, confusion, and irritability, and they’re treated by eating fast-acting carbohydrates like glucose tablets or juice. Severe hypoglycemia, where you can’t treat yourself, requires emergency glucagon.
Glucagon is a hormone that signals the liver to release stored sugar into the bloodstream. Several forms are now available. Nasal glucagon is a dry powder sprayed into one nostril (no inhalation needed) and works within about 15 minutes. An auto-injector version works like an EpiPen and is given in the thigh, abdomen, or upper arm. Traditional glucagon kits require mixing a powder with liquid before injecting, which can be difficult for a bystander in a crisis. The newer ready-to-use options were designed to solve that problem. Anyone who lives with or regularly cares for someone with type 1 diabetes should know where their glucagon is stored and how to use it.
Long-Term Complications
Prolonged high blood sugar damages small and large blood vessels over time. The risk of complications is closely tied to how well blood sugar is controlled and how long someone has had diabetes.
Eye damage (retinopathy) is the most variable complication, affecting anywhere from 16% to 95% of people depending on diabetes duration. Regular eye exams can catch early changes before vision is affected, and treatment can slow or prevent progression. Kidney damage (nephropathy) develops in 30 to 40% of people within 25 years. The earliest sign is small amounts of protein leaking into the urine, though only about 20% of people at that early stage go on to develop more serious kidney disease. Nerve damage (neuropathy), typically starting in the feet and hands with numbness, tingling, or pain, is the most common complication, and up to half of people who have it don’t realize it because it can be painless.
Cardiovascular disease, including heart attack and stroke, is also more common in people with type 1 diabetes. Keeping blood sugar, blood pressure, and cholesterol well managed substantially reduces the risk of all these complications. Advances in glucose monitoring and insulin delivery have made tight blood sugar control more achievable than it was even a decade ago, and complication rates have been declining as a result.