What is high blood sugar?

Hyperglycemia means your blood glucose levels are above the healthy range. Over time, elevated sugar can damage blood vessels, nerves, eyes, kidneys, and the heart. Early recognition and treatment are key to preventing long-term problems.

10 very early signs and symptoms you shouldn’t ignore

1. Excessive thirst (polydipsia)

   When blood sugar is high, the body pulls water from tissues to dilute the glucose. This dehydration triggers persistent thirst that doesn’t fully improve even after drinking.

2. Frequent urination, especially at night (polyuria/nocturia)

   Excess glucose spills into urine and drags water with it. You may notice larger urine volumes and waking up to urinate multiple times overnight.

3. Unusual fatigue or low energy

   Even with high sugar in the blood, your cells may struggle to use it efficiently. The result is a sluggish, “worn out” feeling despite adequate sleep.

4. Increased hunger (polyphagia)

   Cells not getting enough usable energy can leave you feeling hungrier sooner after meals, sometimes alongside weight changes.

5. Blurred vision that comes and goes

   High glucose can change the eye’s lens shape by shifting fluid balance, causing temporary blurriness that often fluctuates during the day.

6. Dry mouth and itchy, dry skin

   Dehydration from frequent urination can lead to cotton mouth, cracked lips, and generalized skin dryness or itchiness.

7. Recurrent infections

   Elevated sugar helps germs thrive and impairs immune defenses. Watch for frequent gum trouble, skin infections, urinary tract infections, or yeast infections (thrush), especially genital yeast infections.

8. Slow-healing cuts or frequent skin irritation

   High glucose can slow circulation and wound repair. Minor nicks and scratches may take longer to close or become easily irritated.

9. Unexplained weight loss

   More common in type 1 diabetes or significantly uncontrolled type 2. If the body can’t use glucose properly, it burns fat and muscle for fuel, leading to weight loss despite normal or increased eating.

10. Dark, velvety skin patches (acanthosis nigricans)

    Thickened, darker skin on the back of the neck, armpits, or groin can be an early sign of insulin resistance and a red flag for developing prediabetes or diabetes.

Subtle cognitive and mood changes—such as brain fog, headaches, irritability, or difficulty focusing—may accompany the above symptoms, often due to dehydration or glucose swings.

Who is most at risk?

• Family history of type 2 diabetes
• Overweight or obesity, especially central (abdominal) fat
• Sedentary lifestyle, poor sleep, high stress
• History of prediabetes or gestational diabetes
• Polycystic ovary syndrome (PCOS)
• High blood pressure or abnormal cholesterol levels
• Older age (risk rises after 35–40 years, but can occur earlier)
• Certain ethnic backgrounds with higher risk (e.g., South Asian, African, Hispanic/Latino, Indigenous)

Special situations

Children and teens

Watch for bedwetting after previously being dry at night, sudden weight loss, extreme thirst, and fatigue. Rapid onset with vomiting or deep breathing can signal an emergency.

Pregnancy (gestational diabetes)

Similar symptoms can occur, but sometimes there are none. Routine screening between 24–28 weeks is recommended; earlier if high-risk.

How doctors confirm high blood sugar

• Fasting plasma glucose: normal <100 mg/dL (5.6 mmol/L); prediabetes 100–125; diabetes ≥126 on two separate days
• HbA1c (3-month average): normal <5.7%; prediabetes 5.7–6.4%; diabetes ≥6.5%
• Oral glucose tolerance test (OGTT): 2-hour value ≥200 mg/dL (11.1 mmol/L) indicates diabetes
• Random plasma glucose ≥200 mg/dL with symptoms suggests diabetes

If you have a home glucometer and consistently see fasting values above 100–125 mg/dL (5.6–6.9 mmol/L) or random values above 180 mg/dL (10 mmol/L) after meals, book a medical evaluation.

What to do if you notice these signs

1. Keep a simple log: symptoms, meal times, sleep, activity, and any home glucose readings.
2. Hydrate: sip water regularly to counter dehydration from high glucose.
3. Move your body: a 10–20 minute walk after meals can help lower post-meal spikes.
4. Prioritize balanced meals: pair carbohydrates with fiber, protein, and healthy fats; limit sugary drinks and refined carbs.
5. Schedule testing: ask your clinician about HbA1c, fasting glucose, or an OGTT.
6. Review medications: some drugs can affect glucose; never stop medicines without guidance.

When to seek urgent medical care

Go to urgent care or the emergency department if high blood sugar is accompanied by any of the following:

• Severe dehydration, confusion, drowsiness, or fainting
• Rapid, deep breathing; fruity-smelling breath; nausea/vomiting; abdominal pain (possible diabetic ketoacidosis)
• Persistent blood glucose readings ≥300 mg/dL (16.7 mmol/L), especially with illness

Prevention and daily steps that make a difference

• Eat intentionally: emphasize vegetables, lean proteins, legumes, whole grains, nuts, seeds; reduce sugary beverages and ultra-processed snacks.
• Be active: aim for 150 minutes/week of moderate activity plus 2 sessions of resistance training.
• Sleep 7–9 hours: poor sleep worsens insulin resistance.
• Manage stress: deep breathing, mindfulness, and regular routines help steady glucose.
• Quit smoking; limit alcohol (and avoid sugary mixers).
• Routine screening if you’re at risk (at least once a year, or as advised).

If you’re on insulin or medications that can cause low blood sugar, consult your clinician before major diet or exercise changes.