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what happens if blood sugar is too high

When blood sugar is too high (called hyperglycemia), it can cause short‑term symptoms and, if it stays high, serious long‑term damage throughout the body.

Quick Scoop

  • Short bursts of high blood sugar can make you feel very thirsty, tired, and need to pee a lot, but are usually not dangerous if they’re rare and corrected quickly.
  • Repeated or long‑lasting high blood sugar can damage blood vessels, nerves, eyes, kidneys, heart, and feet, and can lead to emergencies like diabetic ketoacidosis or diabetic coma.
  • If you have diabetes and your readings are often high, you should contact your doctor or diabetes team to adjust food, activity, or medications.
  • Very high levels with confusion, difficulty staying awake, or trouble breathing are an emergency and need immediate medical help.

What “too high” means

  • High blood sugar is usually called hyperglycemia and is often defined as a blood glucose reading above your personal target range (for many people, this means above about 7 mmol/L before meals, but targets are individual).
  • Occasional small spikes (for example after a big, carb‑heavy meal) can happen to many people and are less concerning than levels that stay high for hours or recur daily.

Think of it like running a car engine too fast: a brief rev is okay; running it red‑lined for hours slowly breaks parts.

What you feel when blood sugar is too high

Common signs and symptoms include:

  • Increased thirst
  • Needing to pee more often
  • Feeling more hungry than usual
  • Feeling very tired or weak
  • Blurred vision
  • More frequent skin infections
  • Cuts and sores that heal slowly

If blood sugar becomes very high, people can also develop:

  • Nausea or vomiting
  • Abdominal pain
  • Deep or fast breathing, fruity‑smelling breath (in diabetic ketoacidosis)
  • Dry, warm skin and signs of dehydration
  • Sleepiness, confusion, or even loss of consciousness

These severe signs are medical emergencies.

What happens inside your body

When blood sugar stays high, extra glucose circulates in your bloodstream and affects many systems:

  • Blood vessels and heart: High glucose damages blood vessel walls, increasing the risk of high blood pressure, heart disease, heart attacks, and stroke.
  • Nerves: Persistent high sugar injures nerves (neuropathy), causing numbness, tingling, burning pain, or loss of feeling, usually in the feet and hands.
  • Eyes: Tiny blood vessels in the retina are damaged (diabetic retinopathy), leading to blurred vision and, over time, possible vision loss or blindness.
  • Kidneys: The kidneys’ filtering units are overworked and damaged (diabetic nephropathy), which can progress to kidney disease and even kidney failure.
  • Feet and skin: Poor blood flow and nerve damage can cause ulcers, infections, and, in severe cases, risk of amputation of toes or feet.
  • Mouth, teeth, and gums: High sugar promotes bacterial growth, raising the chance of gum disease and tooth decay.
  • Digestion: Damage to the vagus nerve can slow stomach emptying (gastroparesis), causing nausea, vomiting, reflux, and unpredictable blood sugar swings.
  • Brain and mental health: Long‑term high sugar and blood vessel changes are linked with cognitive decline, depression, and anxiety.

These problems usually build up slowly over years if blood sugar stays high or is often out of control.

Short‑term dangers: When it becomes an emergency

Two especially dangerous situations can develop from very high blood sugar:

  1. Diabetic ketoacidosis (DKA)
    • More common in type 1 diabetes, but can happen in type 2.
    • Happens when the body can’t use sugar properly and starts breaking down fat rapidly, making acids called ketones.
    • Warning signs: nausea, vomiting, stomach pain, deep or fast breathing, fruity‑smelling breath, extreme thirst, frequent urination, and confusion.
  2. Hyperosmolar hyperglycemic state (HHS)
    • More often in older adults with type 2 diabetes.
    • Blood sugar climbs very high, causing severe dehydration and thickened blood.
    • Warning signs: extreme thirst at first, then dry warm skin, fever, confusion, sleepiness, weakness on one side, problems seeing, or hallucinations.

Both DKA and HHS can lead to coma and are life‑threatening; they require hospital care urgently.

Why controlling high blood sugar matters

Keeping blood sugar in a healthy range can:

  • Reduce the risk of heart disease and stroke
  • Protect your nerves, eyes, and kidneys
  • Lower the chance of foot ulcers and amputations
  • Help you feel more energetic day‑to‑day

Even if you have already developed some complications, bringing high blood sugar under better control often slows their progression.

What to do if your blood sugar is too high

If you already know you have diabetes, common steps doctors recommend include:

  • Checking whether you followed your meal plan, especially carbohydrate and sugary foods.
  • Reviewing whether you took your diabetes medicines or insulin on time and at the right dose, and whether your insulin is in date and stored properly.
  • Staying hydrated with sugar‑free fluids (like water) unless your doctor has given you fluid restrictions.
  • Doing light physical activity if your blood sugar is moderately high and you do not have ketones or feel very unwell (always follow your care team’s advice).

You should contact your healthcare provider if your readings are frequently high, you are unsure how to adjust your treatment, or you notice new symptoms like numbness, vision changes, or slow‑healing sores.

When to seek urgent medical help

Get emergency help right away if:

  • Your blood sugar is very high and you have vomiting, severe abdominal pain, or deep, rapid breathing.
  • You feel very drowsy, confused, or can’t stay awake.
  • You have signs of severe dehydration (very dry mouth, minimal urination, very dry warm skin).
  • You or someone with high blood sugar collapses or cannot respond normally.

These can signal diabetic ketoacidosis or hyperosmolar hyperglycemic state, which are medical emergencies.

Bottom note

Information gathered from public forums or data available on the internet and portrayed here.