15 Early Signs of High Blood Sugar You Shouldn’t Ignore

High blood sugar does not always announce itself with dramatic symptoms. In fact, glucose levels can rise gradually, and some people—especially those developing type 2 diabetes—may notice only subtle changes at first.

Recognizing the early signs of high blood sugar matters because persistent hyperglycemia can affect blood vessels, nerves, kidneys, eyes, and other organs over time. The good news is that blood glucose problems can often be identified with simple tests, giving you and your healthcare provider an opportunity to act before complications develop.

Common symptoms such as frequent urination, excessive thirst, fatigue, and blurred vision occur because excess glucose changes the way your kidneys, tissues, and cells handle water and energy. The American Diabetes Association (ADA) and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) identify increased thirst and urination among the classic signs of hyperglycemia.

Below are 15 early signs of high blood sugar you shouldn’t ignore, what may cause them, and when they warrant medical attention.

Medical disclaimer: This article is for educational purposes only and is not a substitute for diagnosis or treatment from a qualified healthcare professional. Symptoms alone cannot confirm diabetes or hyperglycemia.

What Is High Blood Sugar?

High blood sugar, medically known as hyperglycemia, occurs when glucose builds up in the bloodstream.

Glucose is one of your body’s main energy sources. After you eat carbohydrates, they are broken down into glucose. Insulin, a hormone produced by the pancreas, helps glucose move from your bloodstream into cells where it can be used for energy.

When the body does not produce enough insulin, cannot use insulin effectively, or both, blood glucose may rise.

For many people already living with diabetes, blood glucose above 180 mg/dL is considered high, although individual targets vary depending on age, medications, pregnancy, other medical conditions, and recommendations from a healthcare team.

Hyperglycemia can occur because of diabetes, illness, stress, certain medications, inadequate insulin, or other metabolic factors. A single elevated reading does not necessarily mean you have diabetes.

Why the Early Signs of High Blood Sugar Matter

Persistently elevated glucose can gradually damage small and large blood vessels. Over time, poorly controlled diabetes is associated with complications affecting the eyes, kidneys, nerves, heart, and circulation.

One challenge is that type 2 diabetes may develop slowly. Some people have few or no obvious symptoms during the early stages.

That is why recognizing possible early signs of high blood sugar is useful—but testing is essential. Symptoms such as thirst, fatigue, or blurry vision can have many causes unrelated to diabetes.

If several of the symptoms below occur together or persist, consider discussing blood glucose testing with your healthcare provider.

15 Early Signs of High Blood Sugar

1. Frequent Urination

Urinating more often than usual is one of the most recognizable high blood sugar symptoms.

When glucose becomes elevated, the kidneys work to remove some of the excess glucose through urine. Water follows that glucose, which can increase urine production.

You may notice that you:

• Visit the bathroom more frequently.
• Wake up several times during the night to urinate.
• Produce unusually large amounts of urine.

Frequent urination can also have many other causes, including urinary tract problems, medications, pregnancy, and increased fluid intake. However, when it occurs together with excessive thirst, high blood sugar becomes an important possibility to investigate.

2. Excessive Thirst

Constant thirst, also known as polydipsia, often accompanies frequent urination.

As your body loses more water through urine, you may become dehydrated. Your brain responds by increasing the sensation of thirst.

You might drink a full glass of water and still feel thirsty shortly afterward.

The combination of frequent urination and intense thirst is particularly important because both are recognized classic symptoms of hyperglycemia.

3. Increased Hunger

Feeling unusually hungry even after eating may also occur when glucose regulation is impaired.

This symptom is known as polyphagia.

Glucose may be abundant in the bloodstream, but if insulin is insufficient or the body is resistant to insulin, cells may not use that glucose normally.

As a result, you may notice:

• Hunger shortly after meals.
• Strong food cravings.
• Difficulty feeling satisfied after eating.

Increased appetite alone does not indicate diabetes, but when it occurs with thirst, frequent urination, fatigue, or unexplained weight loss, it deserves attention.

4. Persistent Fatigue

Everyone feels tired occasionally. However, fatigue that continues despite adequate sleep can be one of the early symptoms of high blood sugar.

Glucose is fuel for your cells. When insulin is not working properly, your body may have difficulty using that fuel efficiently.

High glucose can also contribute to dehydration, which may make fatigue worse.

You might notice:

• Low energy throughout the day.
• Difficulty completing normal activities.
• Feeling unusually sleepy after meals.
• Reduced mental or physical stamina.

NIDDK lists tiredness among symptoms that can occur with high blood glucose.

5. Blurred Vision

Suddenly having difficulty focusing may be another warning sign.

Changes in blood glucose can affect fluid levels in structures of the eye, temporarily changing the eye’s ability to focus.

This may cause:

• Blurry vision.
• Vision that seems to fluctuate during the day.
• Difficulty reading.
• Trouble focusing on distant objects.

Blurred vision caused by short-term glucose changes can improve when glucose stabilizes. However, long-term diabetes can also damage the retina.

Any sudden, significant, or persistent change in vision should be evaluated by a healthcare professional.

6. Unexplained Weight Loss

Losing weight without changing your eating habits or activity level should not be ignored.

When the body cannot use glucose effectively, it may begin breaking down stored fat and muscle for energy.

This is particularly important when weight loss occurs alongside:

• Increased hunger.
• Excessive thirst.
• Frequent urination.
• Fatigue.

Unintentional weight loss can have many causes, so medical evaluation is important rather than assuming high blood sugar is responsible.

7. Dry Mouth

A constantly dry or sticky mouth may develop because high glucose can contribute to dehydration.

You may experience:

• A dry tongue.
• Cracked lips.
• Persistent thirst.
• Difficulty swallowing dry foods.
• Bad breath.

Dry mouth can also result from medications, dehydration, mouth breathing, or other health conditions.

If it appears together with frequent urination and intense thirst, checking blood glucose may be worthwhile.

8. Frequent Infections

Recurring infections can sometimes accompany diabetes or sustained hyperglycemia.

People may experience repeated:

• Yeast infections.
• Skin infections.
• Urinary tract infections.
• Gum problems.

High blood glucose can interfere with certain immune functions and create conditions in which some microorganisms grow more easily.

Recurring infections do not automatically mean someone has diabetes, but they can be a reason to discuss screening with a healthcare provider—especially if other signs of high blood sugar are present.

9. Cuts and Wounds That Heal Slowly

A small cut that seems to take unusually long to heal can be another potential clue.

Long-term high blood glucose can interfere with circulation, immune responses, and tissue repair.

Watch for:

• Cuts that remain open longer than expected.
• Recurrent sores.
• Wounds that become red, swollen, or painful.
• Foot injuries that do not heal normally.

People with diagnosed diabetes should pay particular attention to their feet because reduced sensation can make injuries easier to overlook.

Any infected or non-healing wound requires medical evaluation.

10. Tingling or Numbness in the Hands and Feet

Persistent high blood glucose can damage nerves over time, a complication known as diabetic neuropathy.

Symptoms may include:

• Tingling.
• Burning sensations.
• Pins and needles.
• Reduced sensation.
• Numbness.
• Pain in the feet or hands.

Neuropathy generally develops after sustained glucose problems rather than after a single temporary increase. Therefore, tingling or numbness may indicate that abnormal glucose has been present longer than you realized.

Many other conditions can also cause these symptoms, so professional evaluation is important.

11. Dry or Itchy Skin

High blood sugar may contribute indirectly to dry, itchy skin, particularly when frequent urination causes dehydration.

Poor circulation and nerve changes associated with diabetes can also affect the skin.

You may notice:

• Persistent dryness.
• Flaking.
• Itching.
• Cracked skin, particularly on the feet.

Because itching has many potential causes—including allergies, eczema, medications, liver problems, and environmental conditions—it is a less specific sign than excessive thirst or frequent urination.

12. Irritability or Difficulty Concentrating

Changes in glucose levels may affect how some people feel mentally and emotionally.

Possible symptoms include:

• Irritability.
• Difficulty concentrating.
• Feeling mentally sluggish.
• Headaches.
• Changes in mood.

These symptoms are highly nonspecific and can result from stress, lack of sleep, dehydration, anxiety, illness, or many other factors.

However, when they occur alongside classic symptoms of hyperglycemia, checking blood glucose can help determine whether glucose is contributing.

13. Dark, Thickened Skin Around the Neck or Armpits

Darkened, velvety patches of skin—most commonly around the neck, armpits, or groin—may be acanthosis nigricans.

Acanthosis nigricans is not directly caused by one episode of high blood sugar. Instead, it is commonly associated with insulin resistance, which can occur before type 2 diabetes develops.

If you notice new areas of thick, dark skin, especially combined with other diabetes risk factors, talk with your healthcare provider.

Testing may identify insulin resistance, prediabetes, or another underlying condition.

14. Nausea, Vomiting, or Fruity-Smelling Breath

These are not ordinary mild symptoms that should simply be monitored.

Nausea, vomiting, abdominal pain, rapid or deep breathing, severe fatigue, and fruity-smelling breath can indicate diabetic ketoacidosis (DKA).

DKA develops when the body does not have enough insulin and begins breaking down fat rapidly, producing acidic substances called ketones.

It occurs most often in type 1 diabetes, although people with type 2 diabetes can develop it as well.

The CDC identifies increased thirst and urination as earlier DKA symptoms, followed by potentially serious signs including nausea, vomiting, stomach pain, rapid deep breathing, and fruity-smelling breath. DKA can be life-threatening and requires immediate treatment.

15. Sexual Dysfunction

Long-term diabetes can affect blood vessels and nerves involved in sexual function.

Men may experience erectile dysfunction, while women may experience problems such as reduced arousal, vaginal dryness, discomfort, or recurrent genital infections.

Sexual dysfunction is generally not one of the earliest or most specific signs of high glucose. However, unexplained changes may sometimes appear alongside undiagnosed metabolic or cardiovascular problems.

Because many hormonal, psychological, medication-related, neurological, and cardiovascular conditions can affect sexual health, a medical assessment is the best way to identify the cause.

Early Signs of High Blood Sugar at a Glance

Some symptoms are more strongly associated with hyperglycemia than others.

Common symptoms include:

• Frequent urination.
• Excessive thirst.
• Fatigue.
• Blurred vision.
• Increased hunger.
• Unexplained weight loss.

Other possible signs associated with diabetes or prolonged high glucose include:

• Recurrent infections.
• Slow wound healing.
• Tingling or numbness.
• Dry or itchy skin.
• Dry mouth.
• Acanthosis nigricans.

Remember that symptoms cannot tell you exactly what your glucose level is. A blood test is needed for diagnosis.

How Is High Blood Sugar Diagnosed?

Healthcare professionals use standardized laboratory tests to diagnose prediabetes and diabetes.

According to the American Diabetes Association, the following values are used in nonpregnant adults:

Test	Normal	Prediabetes	Diabetes
Fasting plasma glucose	Less than 100 mg/dL	100–125 mg/dL	126 mg/dL or higher
2-hour oral glucose tolerance test	Less than 140 mg/dL	140–199 mg/dL	200 mg/dL or higher
A1C	Less than 5.7%	5.7–6.4%	6.5% or higher

The A1C test estimates average blood glucose over approximately the previous two to three months.

In someone without obvious symptoms, abnormal test results generally need confirmation with repeat testing or another diagnostic test.

A random plasma glucose level of 200 mg/dL or higher in someone with classic symptoms of hyperglycemia can also support a diabetes diagnosis, depending on the clinical situation.

Who Should Be Tested for Diabetes?

You do not need to wait for symptoms before asking about screening.

The ADA’s 2026 Standards of Care recommend beginning testing no later than age 35 for all adults. Testing should also be considered earlier in adults with overweight or obesity who have additional diabetes risk factors.

Risk factors can include:

• Family history of diabetes.
• Prediabetes.
• History of gestational diabetes.
• Polycystic ovary syndrome.
• High blood pressure.
• Abnormal cholesterol or triglyceride levels.
• Physical inactivity.
• Certain medications that affect glucose metabolism.

Your healthcare provider can recommend an appropriate testing schedule based on your individual risk.

When Is High Blood Sugar an Emergency?

High blood sugar is particularly concerning when it is accompanied by ketones, vomiting, breathing problems, confusion, severe dehydration, or inability to keep fluids down.

The CDC recommends checking for ketones when a person with diabetes is sick or has blood glucose at 250 mg/dL or higher.

Seek emergency medical attention if you develop symptoms such as:

• Persistent vomiting.
• Fruity-smelling breath.
• Rapid or deep breathing.
• Severe abdominal pain.
• Confusion.
• Fainting.
• Difficulty breathing.
• High or worsening ketone levels.

The CDC also advises emergency evaluation when blood glucose remains at 300 mg/dL or above along with circumstances suggesting DKA.

Another serious complication, hyperosmolar hyperglycemic state (HHS), is associated with extreme hyperglycemia, profound dehydration, and altered mental status and requires hospital treatment.

Do not attempt to rapidly correct extreme blood glucose levels on your own unless you are following a specific treatment plan provided by your diabetes care team.

What Should You Do If You Notice Early Signs of High Blood Sugar?

If you recognize several symptoms, the most useful next step is not to guess—it is to get tested.

Consider these actions:

1. Schedule a medical appointment. Ask whether fasting glucose, A1C, or another test is appropriate.
2. Track your symptoms. Note thirst, urination, fatigue, weight changes, infections, and other patterns.
3. If you already have diabetes, check your glucose as directed.
4. Take prescribed medications consistently. Do not alter insulin or diabetes medication doses without following your healthcare plan.
5. Stay hydrated. Water is generally a better choice than sugary drinks when glucose is elevated.
6. Know your ketone plan. People at risk of DKA should know when and how to test for ketones.

Exercise can often help improve glucose levels, but there is an important exception: the ADA advises checking for ketones when glucose is above 240 mg/dL, and avoiding exercise when ketones are present because activity can make glucose rise further.

Frequently Asked Questions About Early Signs of High Blood Sugar

What are the first signs of high blood sugar?

The most common early signs include increased thirst, frequent urination, fatigue, and blurred vision. Increased hunger, dry mouth, and unexplained weight loss may also occur.

Some people, particularly those developing type 2 diabetes, may have few or no noticeable symptoms.

How can I tell if my blood sugar is high without a glucose meter?

You cannot reliably determine your glucose level from symptoms alone.

Thirst, frequent urination, fatigue, blurry vision, and dry mouth may suggest hyperglycemia, but these symptoms can occur for many other reasons.

A glucose meter or laboratory blood test is needed to know your actual glucose level.

Can high blood sugar cause headaches?

Headaches can occur when glucose is elevated, potentially in association with dehydration or changes in glucose levels. However, headaches are nonspecific and can have many other causes.

If headaches repeatedly occur together with thirst, frequent urination, blurred vision, or fatigue, consider discussing blood glucose testing with your healthcare provider.

What level of blood sugar is dangerous?

There is no single number that defines danger in every person.

Context matters, including whether you have diabetes, whether ketones are present, how long glucose has been elevated, and whether you have symptoms such as vomiting, confusion, or breathing difficulties.

For people with diabetes, the CDC recommends checking ketones when sick or when glucose reaches 250 mg/dL or higher. Persistent glucose of 300 mg/dL or higher, fruity breath, vomiting, breathing difficulty, or multiple symptoms of DKA warrant emergency medical attention.

Can you have high blood sugar without diabetes?

Yes.

Temporary hyperglycemia can occur during severe illness, physical or emotional stress, and with certain medications such as corticosteroids.

However, repeated high glucose readings should be evaluated because they may indicate prediabetes, diabetes, or another medical problem.

Does high blood sugar always cause symptoms?

No.

Mild or gradually developing hyperglycemia may cause few obvious symptoms. This is one reason screening is important, particularly for people with risk factors for type 2 diabetes.

Is an A1C below 7% always the goal for someone with diabetes?

Not necessarily.

For many adults with diabetes, an A1C goal below 7% is commonly recommended, but targets should be individualized according to factors such as age, pregnancy, medications, other health conditions, and risk of hypoglycemia.

Final Thoughts: Don’t Ignore the Early Signs of High Blood Sugar

The early signs of high blood sugar can be easy to dismiss. You may assume you are urinating more because you are drinking more water, blame fatigue on a busy schedule, or attribute blurry vision to tired eyes.

But when excessive thirst, frequent urination, fatigue, increased hunger, unexplained weight loss, blurred vision, recurrent infections, or slow wound healing persist—especially when several symptoms occur together—it is worth taking them seriously.

You do not need to diagnose yourself based on symptoms. A simple glucose or A1C test can provide far more useful information.

Early detection gives you and your healthcare provider more opportunities to address abnormal blood glucose before complications develop.

If you recognize several of these 15 early signs of high blood sugar, schedule a medical evaluation rather than waiting for symptoms to become severe.

Share this article with someone who may benefit from knowing the warning signs, and speak with a qualified healthcare professional if you are concerned about your blood sugar.

Medical and Editorial Sources

Diagnostic thresholds, screening recommendations, A1C information, and emergency guidance in this article are supported by current information from the American Diabetes Association, NIDDK, and CDC.

The symptom framework was also developed from the source material supplied for this article.