What Are the Symptoms of High Blood Sugar?

High blood sugar symptoms can be subtle at first; left untreated, they can have a serious impact on your health.

Hyperglycemia is the term for high blood sugar, a common condition of diabetes. 

Glucose, or blood sugar, comes from the food you eat and is your body's main source of energy. Glucose naturally rises and falls throughout the day. Insulin, a hormone, helps regulate this process by taking glucose from the blood and into cells for energy. 

But when you don’t produce any or enough insulin or it is not being used efficiently, glucose remains in the blood and blood sugar levels rise. 

If not treated, high blood sugar can cause life-altering complications such as heart disease and vision loss. Understanding symptoms of high blood sugar can assist in early detection and treatment of the condition, which can prevent complications of diabetes. 

An illustration of a woman drinking water

Illustration by Zoe Hansen for Health

High Blood Sugar Symptoms

The typical blood sugar target for someone with diabetes who has not yet eaten is 80 to 130 milligrams per deciliter (mg/dL). Within two hours of starting a meal, the level should be less than 180mg/dL. Blood sugar is typically considered high when the levels are over these thresholds. 

Keep in mind that your blood sugar targets may be different based on factors like age and other health conditions you may have. The targets are also different for people without diabetes.

Testing your blood sugar levels, such as with a glucometer, is the main way to tell if your blood sugar is too high. However, even before you check your levels, you may experience symptoms of high blood sugar.

Excessive Thirst

Feeling like you can't quench your thirst regardless of how much you drink is a common symptom of high blood sugar. The medical term for this is polydipsia.

Usually, the kidneys reabsorb glucose and send it back to the bloodstream. When blood sugar is high, that extra glucose is released through urine. Glucose actually pulls water into the urine, causing the body to lose even more fluids. The thirst you experience is your body trying to make up for the extra fluid that was lost in your urine.

Excessive thirst can increase the risk of dehydration. Being dehydrated for a long time can cause nausea, dizziness, headache, and fainting. Extreme dehydration can also make blood sugars rise even higher since less urine and, in turn less glucose, is being emptied.  

Increased urination leads you to want to drink more. You may turn to sweetened beverages. Drinking large amounts of sweetened beverages that are rich in carbohydrates, such as juice, soda, and other sweetened beverages, can make blood sugars rise higher.

Excessive Urination

Excessive urination goes hand-in-hand with excessive thirst. The thirstier you are, the more you drink. The more you drink, the more you urinate. This increase in urination is known as polyuria.

The increase in urination is also due to your body having to rid itself of more liquid not just from what you drink, but also from the high levels of glucose: Because glucose gets eliminated in the urine when blood sugar is high, there is more liquid for your body to get rid of.

The increased need to urinate often occurs in the middle of the night. In children with type 1 diabetes, this may present in the form of bed-wetting. Even a child who is toilet trained may start wetting the bed.

Extreme Hunger

Someone with high blood sugar might have to eat a lot of food before feeling full. This increase in hunger is known as polyphagia. 

As excess glucose is let out in urine, the calories that the glucose contained is let out too. That means you are not taking in the calories, leading to hunger. You eat more to make up for those lost calories and to quiet the hunger.


Extreme fatigue or tiredness occurs because your body is unable to use the food you are eating for energy. You get glucose from the food you eat. That glucose is used for energy. Insulin is what moves the glucose to cells to make that energy. 

But a lack of insulin means glucose is staying in the blood instead of being moved to cells and used as energy. This causes your blood sugar to get high. And because your glucose isn’t being used for energy, you may feel very tired and sleepy.

Unexplained Weight Loss

Weight loss that is not due to any other health condition or a lifestyle change can be an early sign of high blood sugar. Glucose is supposed to be used for energy. When it can’t be, it instead builds up in the bloodstream and leads to high blood sugar. The body still needs a way to get energy, though, and so the energy is instead pulled from muscle and fat. As muscle and fat start to get burned for energy, you can lose weight.  

Blurry Vision

High blood sugar can change the fluid levels in your eyes. If there is too much sugar and water in your eyes’ lenses, the lenses can’t change shape. This can cause your vision to be blurry. 

High blood sugar can also cause swelling in the tissues of your eyes that help you focus, leading to blurriness. 

This blurred vision is usually temporary and will clear up when your blood sugar levels are brought back to normal levels.

However, long-term high blood sugars can cause permanent damage. Chronic hyperglycemia can damage the small blood vessels in the eyes. One condition that this blood vessel damage can lead to is diabetic retinopathy.

At first, diabetic retinopathy can, from time to time, make it hard to read or to see objects in the distance. In its later stages, the condition can cause not only blurry vision, but also floating spots in your vision, vision loss, and even blindness. 

Because of the potential serious effects to the eyes, the American Diabetes Association recommends that all people newly diagnosed with type 2 diabetes receive a dilated eye exam from an ophthalmologist or optometrist shortly after diagnosis and every year thereafter. It’s recommended that people with type 1 diabetes receive a dilated eye exam within five years of a diagnosis and every year after that.

Numbness and Tingling in the Extremities

Numbness and tingling in the hands and feet can occur when a person has poor circulation due to an accumulation of glucose. 

In addition, chronically elevated blood sugars can damage the nerves. This condition is known as diabetic neuropathy. There are different types of diabetic neuropathy, each of which can affect different parts of the body. But the most common type is peripheral neuropathy, which affects the feet and legs and sometimes the hands and arms.

This symptom is more common in people who have had diabetes for a long time, affecting about half of people with diabetes.

Frequent Infections

High blood sugars may contribute to frequent infections due to a disruption in the body's immune response. Researchers also believe certain bacteria grow better in a high-sugar environment. 

High blood sugar may contribute to an increased risk of not only bacterial infections, but also yeast infections. In particular, infections of the respiratory and urinary tracts are especially common for people with diabetes.

Skin Problems

Hyperglycemia can cause a number of skin changes, including:

  • Dry or itchy skin
  • Frequent skin infections
  • Wounds that are slow to heal

Sexual Dysfunction

Chronically elevated blood sugars can eventually lead to nerve damage in the genitals. For example, high blood sugar can damage the nerves that are needed to maintain an erection.

Hyperglycemia is associated with sexual dysfunction in people with female reproductive organs as well, but more research is needed to more clearly understand the link.

Reduced Fertility

If you have diabetes and are trying to become pregnant, having difficulty conceiving could be a sign of high blood glucose, as it can lead to reduced fertility and egg quality. It's important to continue monitoring and managing your blood glucose levels if you're trying to become pregnant, as well as throughout a pregnancy. In women with pre-existing diabetes, elevated blood sugar levels during the first few weeks of pregnancy can raise the risk for miscarriages or congenital disorders in the fetus later in the pregnancy.

Also, some studies of men with type 1 diabetes suggest that hyperglycemia may negatively impact sperm production, size, movement, and quality—all of which are linked to reduced fertility and infertility.

Mood Changes

Understanding the direct impact that high blood sugar has on mood is difficult to measure accurately, but many people with diabetes self-report that extreme fluctuations in blood sugar—high or low—can cause changes in mood and behavior.

In a review of the literature, researchers found a significant association between a higher rate of after-meal glucose increase and more negative mood symptoms. However, they suggest the current evidence is not clear and that the relationship needs higher-quality research.

Signs of a High Blood Sugar Emergency 

If high levels of blood sugar aren’t treated, you can develop a life-threatening complication called diabetic ketoacidosis (DKA). The condition—which is more common in type 1 diabetes—can cause a build-up of ketone, a type of acid, in your blood.

Sometimes, DKA can be the first sign of diabetes for those who have not yet been diagnosed. 

DKA can develop slowly at first, with its initial symptoms including: 

  • Thirst 
  • A very dry mouth
  • Frequent urination

The condition can worsen quickly, with later symptoms including: 

  • Headache
  • Vomiting
  • Deep, shallow breathing
  • Fruity breath
  • Stomachache
  • Muscle aches and stiffness

Left untreated DKA, can result in coma or death. 

High blood sugar levels mixed with dehydration can also lead to hyperglycemic hyperosmolar state (HHS). HHS is more common among people with type 2 diabetes who have had an infection of some kind, such as pneumonia or a urinary tract infection.

HHS can present as extremely high blood sugars (600mg/dL) with fever, confusion, or weakness or paralysis on one side of the body. Immediate treatment is necessary to prevent serious consequences.

When to See a Healthcare Provider

If you have diabetes and experience a randomly high blood sugar from time to time, there is usually no need to panic. Try to understand what changes could have triggered a blood sugar spike, whether by looking at your diet or activity levels. Knowing the reason behind high blood sugar helps you figure out how to prevent it from happening again. 

On the other hand, if you have been experiencing high blood sugars regularly, you may need a change in your treatment plan. This doesn't mean you haven’t been managing your diabetes well. Rather, diabetes is a progressive disease that can change how it affects you over time. That means changes to things like medications, meal plans, and exercise regimens might be needed to help you achieve better control over your blood sugar levels.

If you do not have diabetes and suspect that you are experiencing high blood sugar, consider making an appointment with a healthcare provider.

Regardless of whether you have been diagnosed with diabetes, you should also seek care if you are experiencing any symptoms of DKA or HHS. For both conditions, quick treatment is crucial.

A Quick Review

Hyperglycemia can present itself in many ways. When glucose cannot be used as energy and instead builds up in the blood, the body naturally tries to compensate. As your body does this, you can experience classic symptoms of high blood sugar such as increased thirst, increased hunger, and increased urination. Some of the other signs, like weight loss, blurry vision, skin conditions, and frequent infections may seem less obvious. 

If you have diabetes and are experiencing any symptoms of hyperglycemia, you may need a change in your treatment plan to get your blood sugars back in a healthy range.

If you do not have diabetes but are experiencing symptoms of hyperglycemia, reach out to a healthcare provider for screening. Early detection and treatment can help to delay and manage diabetes and diabetes-related complications. 

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