What Is Diabetes? Symptoms and Causes

Diabetes is a disease that develops when your body’s cells have trouble using glucose (its preferred form of sugar) to make energy. This causes your blood sugar levels to rise, leading to diabetes symptoms. The Centers for Disease Control and Prevention (CDC) estimates that there are more than 37 million Americans living with diabetes.1

Several different types of diabetes exist, each with different causes. However, all are related in that they cause high blood sugar levels. If left untreated, you may eventually develop other health complications due to damage to your blood vessels and nerves.

The Role of Insulin in Diabetes

When you eat, your body breaks food down into glucose, which enters your bloodstream. For your cells to take up glucose and use it for energy, they need insulin, a vital hormone made by specialized cells in your pancreas known as beta cells. With diabetes, your body may not make enough insulin, or your cells don’t know how to properly use it (known as insulin resistance).2

Types of Diabetes

There are three main types of diabetes — type 1 diabetes (T1D), type 2 diabetes (T2D), and gestational diabetes. A condition known as prediabetes is when you have elevated blood sugar levels, but not high enough to be diagnosed as diabetes. Other less common types of diabetes include type 3c diabetes (caused by a variety of diseases of the pancreas) and latent autoimmune diabetes in adults (LADA).

Type 1 Diabetes

T1D is a disease in which your pancreas no longer makes insulin. Without insulin, your body’s cells can’t take up glucose from your blood to use for energy. As a result, your blood sugar levels rise and eventually become high enough that you start to have symptoms. Researchers and doctors believe T1D is an autoimmune condition that causes your body’s immune system to attack and damage beta cells in the pancreas to the extent that they can’t produce insulin anymore. T1D is treated with insulin therapy, usually using an insulin pump or injections with a needle and syringe or an insulin pen.3

Type 2 Diabetes

In T2D, your body’s cells are resistant to insulin’s effects, preventing them from taking up glucose and using it for energy. This causes your blood sugar levels to rise over time. As a result, your pancreas tries to make more insulin to compensate for the increase in blood sugar, but eventually it can’t keep up with your body’s needs. T2D medications focus on:

  • Stimulating the pancreas to make more insulin
  • Helping your cells become more sensitive to insulin
  • Preventing your liver from making more glucose
  • Helping your kidneys get rid of excess glucose from your bloodstream

In more severe cases of T2D, doctors may prescribe insulin therapy in addition to these medications to boost their effects.4

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Gestational Diabetes

Gestational diabetes develops in pregnant women who weren’t previously diabetic. This is a temporary form of diabetes that typically goes away after you give birth. During pregnancy, you experience many hormonal changes. Some of these may cause weight gain, making your body’s cells less sensitive to insulin and unable to use it as efficiently to take glucose from your blood, causing your blood sugar level to rise. Gestational diabetes is a risk factor for developing T2D — in fact, around 50% of women with the condition will go on to develop T2D.

Pregnant women can control gestational diabetes with dietary changes and an exercise plan that is safe during pregnancy. If these changes don’t help control your blood sugar, your doctor may prescribe certain diabetes medications or insulin therapy.5


Prediabetes is a condition in which your blood sugar level is elevated, but not enough to be considered T2D. In prediabetes, your cells are starting to become resistant to insulin, making it less effective. Your pancreas may also try to compensate by making more insulin, but it can’t meet demand as your blood sugar rises. Having prediabetes increases your risk of T2D, along with heart disease and stroke. Fortunately, the condition is completely reversible with proper lifestyle changes, including diet and exercise. Losing around 5% of your body weight has also been shown to help reduce your risk of prediabetes progressing to T2D.6

Other Types of Diabetes

Other, less common types of diabetes include type 3c diabetes and LADA. Type 3c diabetes is when an injury or illness prevents your pancreas from making insulin. This can be caused by pancreatitis (inflammation in the pancreas), pancreatic cancer, hemochromatosis (too much iron in the blood and the organs of the body, including the pancreas), or cystic fibrosis. Type 3c diabetes is typically managed with insulin therapy and medications used to treat T2D.7

An autoimmune condition causes LADA, also known as type 1.5 diabetes. It looks similar to T1D, but develops slowly over the course of many years. Most people who develop LADA are 30 years or older, and are often misdiagnosed with T2D. It can be treated with insulin therapy.8

What Causes Diabetes?

Anyone can develop diabetes, but certain factors increase your risk. These vary depending on the type of diabetes.

Type 1 Diabetes Causes

T1D is a less common form of diabetes, affecting only 5% to 10% of people with diabetes. It was originally referred to as juvenile diabetes because the disease was thought to mainly occur in children, teens, and young adults. However, it’s now known that you can develop T1D at any age.3

Doctors and researchers believe autoimmunity in T1D may be triggered by infection with certain viruses. Parents can also pass down genes that increase their children’s risk of developing the disease. However, just because you have the genes doesn’t necessarily mean you’ll go on to develop T1D. There’s no way to prevent T1D, unlike T2D.9

Other risk factors for developing T1D include:10

  • Injury to your pancreas caused by a surgery, accident, tumor, or infection
  • Physical stress caused by illness or surgery
  • The presence of autoantibodies (antibodies made by your immune system that recognize your tissues and organs as foreign)

Type 2 Diabetes Causes

T2D is much more common than T1D, accounting for 90% to 95% of diabetes cases. It tends to develop in people ages 45 and older, but is becoming more common in children, teenagers, and young adults.4

So, how do you get diabetes? Your risk for developing T2D increases if you have any of the following factors:11

  • Excess weight or obesity
  • High blood pressure
  • Low levels of “good” (HDL) cholesterol
  • High triglyceride (fat) levels
  • A family member (parent, brother, or sister) who also has prediabetes or T2D
  • Previous case of gestational diabetes, or if you gave birth to a baby who weighed nine pounds or more
  • Getting exercise less than three days per week
  • Being a smoker
  • Family history of heart disease or stroke
  • Polycystic ovarian syndrome (PCOS)
  • Being of African American, Hispanic/Latino, Native American, Asian American, or Pacific Islander descent
  • Having non-alcoholic fatty liver disease

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Gestational Diabetes Causes

Gestational diabetes affects between 2% to 10% of pregnancies every year in the United States.5 Your risk of gestational diabetes increases if you:9

  • Are overweight
  • Have had gestational diabetes in a previous pregnancy
  • Have a family history of T2D
  • Have PCOS
  • Have given birth to a baby weighing 9 pounds or more
  • Are 25 years or older
  • Are of Hispanic/Latino, African American, Alaska Native, Pacific Islander, American Indian, or Native Hawaiian descent

Symptoms and Signs of Diabetes

Diabetes symptoms are your body’s response to high blood sugar levels. These include:12

  • Feeling very thirsty and hungry
  • Urinating frequently, especially at night
  • Losing weight without meaning to
  • Feeling numbness or tingling in your hands or feet
  • Having sores or wounds that heal slowly
  • Having blurry vision
  • Having very dry skin
  • Having more infections than normal

The onset of diabetes symptoms can depend on the type of diabetes you have. For example, once your pancreas stops making enough insulin, T1D symptoms can develop quickly over the course of a few days or weeks. You may also experience stomach pain, nausea, or vomiting before a T1D diagnosis. On the other hand, T2D symptoms develop over the course of several years, and some people may not notice any at all. If you’re at an increased risk of developing T2D, tell your doctor so they can monitor you for any changes in your blood sugar levels.

Gestational diabetes typically doesn’t have any associated symptoms. The condition tends to develop around the 24th week of pregnancy in your second trimester. To diagnose this type of diabetes, your doctor will test you for gestational diabetes between your 24th and 28th weeks of pregnancy.

Diabetic Ketoacidosis

Diabetic ketoacidosis (DKA) is a serious health complication that may occur before a T1D diagnosis. However, people with T2D can also be diagnosed with DKA if their blood sugar levels rise too high or if they are taking certain diabetes medications.13

DKA develops when your body doesn’t make enough insulin for your cells to take glucose up from your bloodstream. As a result, your blood sugar levels rise steadily. Since your cells need a way to make energy, your liver begins to break down stored fats. This process produces ketones, which make your blood very acidic. The buildup of ketones can become dangerous quickly. You can test for ketones with a test strip and a few drops of urine. If you notice any of the following symptoms, be sure to seek medical attention immediately:

  • Headache
  • Fruity smelling breath
  • Feeling very tired
  • Stomach pain
  • Nausea and vomiting
  • Dry mouth and skin
  • Fast, deep breathing
  • Stiff or achy muscles

DKA is treated using insulin and by replenishing your body with fluids and electrolytes. These help lower your blood sugar back into a normal range.

How Is Diabetes Diagnosed?

Doctors diagnose diabetes using a simple blood test that’s quick and readily available. You may have to fast before your test, meaning you can’t eat for at least eight hours before having your blood drawn.14

Fasting blood sugar levels can tell your doctor if you have diabetes. Another test can also measure your hemoglobin A1C (HbA1c), which is your average blood sugar level over the past three months. This is reported as a percentage, since it refers to the percentage of your red blood cell proteins with glucose bound to them. The CDC breaks down the potential results of these tests:

  • Normal — fasting blood sugar of 99 mg/dL or lower; HbA1c below 5.7%
  • Prediabetes — fasting blood sugar of 100 to 125 mg/dL; HbA1c between 5.7% to 6.4%
  • Diabetes — fasting blood sugar of 126 mg/dL or higher, HbA1c 6.5% or above

Your doctor may also order an oral glucose tolerance test (OGTT). For this test, you’ll fast and have a blood sample taken. You’ll then drink a very sweet glucose solution, and have blood samples taken at one, two, and three hours afterward. Your blood sugar level at the two-hour mark will tell your doctor if you have diabetes. The results of the OGTT are as follows:

  • Normal — 140 mg/dL or lower
  • Prediabetes — 140 to 199 mg/dL
  • Diabetes — 200 mg/dL or higher

Complications of Diabetes

Over time, high blood sugar levels from diabetes can lead to several health complications, including eye problems, kidney problems, and nerve damage. This is because the blood vessels and nerves in the body become damaged by excess glucose in your bloodstream. Managing your diabetes with insulin, medications, and lifestyle changes can help prevent these complications and help you lead a healthier life.

Eye problems caused by diabetes include diabetic retinopathy (DR), glaucoma, and cataracts. DR affects the blood vessels that feed the retina, or light-sensitive tissue at the back of your eye. Glaucoma impacts your eye’s ability to drain fluid, causing pressure to build. Cataracts are caused by clouding of the clear lens that covers your eye. If left untreated, all of these conditions can cause vision loss. Be sure to go to your regularly scheduled eye exams so your eye doctor can monitor for these complications.15

Diabetes can also damage the delicate blood vessels in your kidneys, preventing them from properly filtering out waste and excess fluid. You may develop a condition known as diabetic nephropathy, or kidney damage. If left untreated, it can progress to chronic kidney disease (CKD).16

Finally, high blood sugar levels can damage the nerves throughout your body. You may notice numbness, pain, or a “pins and needles” tingling sensation in your feet or hands. This is known as peripheral neuropathy, and is common in people with diabetes. You may also develop autonomic neuropathy, which affects the nerves that help control your internal organs. You may notice you have bladder or bowel problems, sexual dysfunction, increased sweating, or digestive problems.17

Resources for Living With Diabetes

If you’re living with diabetes, online resources can help you learn more about medications, managing the condition, and how to find support.

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Frequently Asked Questions (FAQ) About Diabetes

Got questions about diabetes? Read more below to learn about some of the most common questions people with diabetes ask. If you still have questions, be sure to talk to a doctor who understands your specific case and needs.

Can diabetes be reversed?

Depending on the type of diabetes you have, you may be able to reverse it. T1D is an autoimmune disease that permanently damages the beta cells in your pancreas. These cells are responsible for making insulin. For this reason, you can’t reverse or cure T1D.18 You’ll have to use insulin for the rest of your life. Some people may qualify for a pancreas transplant or a pancreatic islet transplant (tissue that contains beta cells). However, it can be difficult to qualify for these transplants and you have to take medications to stop your immune system from rejecting the transplant.19

On the other hand, prediabetes and T2D are reversible through making diet and lifestyle changes. Losing weight by exercising and eating a healthy diet can help make your cells more sensitive to insulin, allowing them to use extra glucose in your bloodstream. Weight loss (bariatric) surgery has also been shown to help people reverse T2D and prediabetes.20

Gestational diabetes typically resolves itself once you give birth to your baby.

Does sugar cause diabetes?

This is a common myth, but the truth is that sugar doesn’t cause diabetes.21 Sugar that comes from carbohydrates in starchy or sugary foods gets broken down into glucose in your body. Your body uses glucose no matter what foods it came from. However, eating an excess of sugar can lead to weight gain, which may increase your risk for developing diabetes.

Adults in the United States consume an average of 77 grams of sugar per day, which is much higher than the recommended amount from the American Heart Association (AHA).22 The AHA suggests no more than 36 grams per day for men and 25 grams per day for women. To help avoid developing diabetes, try to limit the amount of sugary food and drinks you consume, which include sodas, sports drinks, candy, cookies, and other sweets.

Do I need to take insulin for the rest of my life?

If you’re living with T1D, you’ll need to take insulin for the rest of your life. This is because your pancreas doesn’t make enough or any insulin, which your body needs to convert glucose into energy.18 You can manage T2D with other medications besides insulin, but sometimes it’s useful for treating severe cases of the disease. You may also need insulin if you have gestational diabetes, but you shouldn’t need it once you give birth.

How often do I need to check my blood sugar?

How often you check your blood sugar depends on the type of diabetes you have and the medications you are taking. (For instance, patients taking sulfonyureas for type 2 diabetes need to check their blood sugars more than other people with T2D because of the risk of hypoglycemia from using these older agents.) Checking your blood sugar level can help you make sure you’re keeping it within a healthy range. This helps prevent other health complications later on. It can also help you learn how well a new diabetes medication is working, and understand how different factors can affect your levels, such as illness, exercise, diet, and stress.23

If you have T1D, it’s recommended to test your blood sugar between four to 10 times per day. You may test:

  • Before eating meals or snacks
  • Two hours after eating meals or snacks
  • Before going to bed
  • Before and after exercising
  • During the night as needed
  • When you’re sick
  • If you’ve started a new medication
  • If you’ve made any major changes to your daily routine

If you have T2D, your doctor may recommend testing several times a day to make sure your blood sugar stays within a healthy range. The number of times you test generally depends on the type of insulin or other medications you’re using, if any. If you inject insulin multiple times a day, you should test before eating meals and at bedtime. If you use an intermediate- or long-acting insulin that lasts several hours to several days, you may only need to test before breakfast or before bed.

Recently patients with T1D (and some with T2D) have been using continuous glucose monitoring systems that can tell you what your glucose level is every five minutes or so. This avoids having to do so much fingerstick testing.31

What are the signs of low blood sugar (hypoglycemia)?

Low blood sugar, also known as hypoglycemia, can have a number of causes, including:24

  • Taking too much insulin
  • Exercising
  • Drinking alcohol
  • Not eating enough carbohydrates to counteract the amount of insulin you took
  • Hot, humid weather
  • Having your period (menstruation)
  • Traveling to a high altitude for an extended period of time
  • Going through puberty

You have hypoglycemia when your blood sugar falls below 70 milligrams per deciliter (mg/dL) of blood. Symptoms include:

  • Shaking
  • Sweating
  • Rapid heartbeat
  • Dizziness
  • Hunger
  • Confusion or irritability
  • Anxiety or nervousness

To treat hypoglycemia, the CDC recommends using the 15-15 rule. If your blood sugar is between 55 to 69 mg/dL, eat 15 grams of carbohydrates, wait 15 minutes, then test your blood sugar. You can drink fruit juice, eat hard candies, or use glucose tablets to help raise your blood sugar.25  If your sugar is below 55 mg/d, or if you are becoming confused, you may need to use (or have help using) a glucagon nasal spray or injection.32

What are the signs of high blood sugar (hyperglycemia)?

High blood sugar, also known as hyperglycemia, can be caused by:26

  • Not taking your diabetes medications or using enough insulin
  • Using expired insulin
  • Not injecting insulin properly
  • Failure of an insulin pump to deliver insulin, such as with a kink in the tubing
  • Not following a low-carbohydrate diet
  • Experiencing stressful situations
  • Injury or surgery
  • Having an infection or illness

Symptoms of hyperglycemia include:

  • Feeling thirsty
  • Blurry vision
  • Feeling tired or weak
  • Frequent urination

To help manage hyperglycemia, be sure to take the correct amount of insulin when taking account of what you’re eating. Do not skip doses of insulin or your diabetes medication, as this can lead to severely high blood sugar levels and potentially DKA. Try to stick with your diabetes eating plan as well by limiting your carbohydrate intake.

Can diabetes cause hearing loss?

Much like other forms of nerve damage caused by high blood sugar levels, diabetes can also cause hearing loss by damaging the nerves in your inner ear. Interestingly, low blood sugar levels can impact hearing by affecting how nerves send signals from your inner ear to your brain.27

According to the CDC, hearing loss affects people twice as much with diabetes compared to those without. Prediabetes can also increase the risk of hearing loss by 30% compared to people with healthy blood sugar levels.

If you begin to notice these signs of hearing loss, talk to your doctor:

  • Trouble hearing conversations where multiple people are talking
  • Asking people to repeat themselves often
  • Trouble hearing in busy or noisy places with lots of background noise
  • Turning the TV volume up too loud for others in the room
  • Thinking people are mumbling when they’re talking at a normal volume
  • Trouble hearing people with quiet voices, or small children

While hearing loss is irreversible, you can take steps to help protect your hearing and ears, including visiting an audiologist every year. They can monitor your hearing for any loss. You can also avoid loud noises, which may damage your ears. Monitoring and controlling your blood sugar levels can help prevent more hearing loss.

Can diabetes cause hair loss?

In some cases, diabetes can cause hair loss. High blood sugar levels can damage the blood vessels that bring oxygen and nutrients to your hair follicles, causing your hair to fall out. People with T1D are more likely to have a condition known as alopecia areata (AA). In AA, the immune system recognizes your follicles as foreign, so it attacks them, which can cause your hair to fall out.28

How does diabetes affect my mental health?

Living with diabetes can be stressful — you may be getting used to injecting yourself with insulin, or worrying about following a new diet or how you’re going to manage your blood sugar. Stress causes your body to release the hormone cortisol, which can make your blood sugar levels change rapidly. Stress from being sick or injured can also cause your levels to rise. According to the CDC, people living with diabetes are 20% more likely to experience anxiety compared to those without. To help manage your stress and anxiety, you can practice yoga or meditation, take some time to yourself, or get active. If you find that your anxiety is interfering with your daily activities and responsibilities, talk to your doctor.29

Depression is a mental health condition that affects people with diabetes two to three times more than people without diabetes. However, only one-quarter to one-half of people with diabetes and depression receive a diagnosis and proper treatment, so it’s important to recognize the signs of depression and seek help from a mental health professional. Symptoms of depression can vary from mild to severe, and include:

  • Having trouble falling asleep or sleeping too much
  • Feeling empty or sad
  • Losing interest in activities you normally enjoy
  • Feeling extremely tired or fatigued
  • Having difficulty making decisions or concentrating
  • Feeling anxious, guilty, hopeless, or irritable
  • Not eating at all or overeating
  • Having unexplainable headaches, digestive problems, cramps, aches, or pains
  • Having thoughts of harming yourself, suicide, or death

If you have any of these symptoms, talk to your doctor right away so you can get treatment.

How does gestational diabetes affect my baby?

Properly managing gestational diabetes with diet, exercise, and medication helps ensure your baby stays healthy during your pregnancy. However, unmanaged gestational diabetes can lead to a condition known as macrosomia, or a baby with an excessive birth weight. If your blood sugar is too high and you don’t have enough insulin, the extra glucose can cross the placenta to your baby. Your baby’s pancreas will try to make extra insulin to help lower their blood sugar. The extra energy from the glucose causes your baby to store fat.30

At birth, your baby may have low blood sugar because they make more insulin to compensate. They may also be at a higher risk for breathing problems and damaging their shoulders during birth. In addition, studies show that babies born making extra insulin are at a higher risk for obesity and developing T2D.