High blood sugar often develops without obvious warning signs. Symptoms typically don’t appear until blood sugar rises above 180 to 200 mg/dL, which means you can have elevated levels for weeks or months without realizing it. The most reliable way to know is testing, but your body does send signals worth recognizing.
The Earliest Symptoms to Watch For
The first signs of high blood sugar tend to be subtle enough that people dismiss them as stress, aging, or not drinking enough water. The classic early symptoms are increased thirst, frequent urination, blurred vision, and unusual fatigue. These four tend to travel together, and there’s a logical chain connecting them.
When excess glucose builds up in your bloodstream, your kidneys work harder to filter it out. That pulls extra water from your body into your urine, which is why you pee more often. Losing that fluid makes you thirsty. Meanwhile, your cells aren’t getting the glucose they need for energy (even though there’s plenty floating in your blood), so you feel tired despite eating normally. High blood sugar also causes the lens of your eye to swell slightly, which shifts your focus and makes vision blurry.
Increased hunger is another early sign. Your body is essentially surrounded by fuel it can’t use, so it keeps asking for more.
Signs That Build Over Time
If blood sugar stays elevated for weeks or longer, additional symptoms start stacking up. These are the ones that often prompt people to finally get checked.
Unexplained weight loss. This sounds counterintuitive since high blood sugar is linked to eating more, not less. But when glucose can’t enter your cells properly, your body thinks it’s starving. It compensates by burning fat and muscle at a rapid pace, which can cause noticeable weight loss even if your appetite has increased.
Slow-healing cuts and wounds. Elevated blood sugar impairs circulation, which means the nutrients and oxygen your skin needs to repair itself don’t arrive efficiently. It also suppresses parts of your immune response and encourages bacterial growth, making even minor cuts or scrapes take significantly longer to heal or become infected more easily.
Frequent infections. Yeast infections, urinary tract infections, and skin infections become more common because the excess sugar in your blood and tissues creates a favorable environment for bacteria and fungi. Recurring infections, particularly in someone who doesn’t usually get them, can be an overlooked clue.
Tingling or numbness in your hands and feet. Prolonged high blood sugar damages small nerve fibers, starting at the extremities. This often feels like pins and needles, burning, or reduced sensation in the fingers and toes.
Skin Changes You Can See
Your skin sometimes reveals high blood sugar before a blood test does. One visible sign is acanthosis nigricans: dark, velvety patches of skin that appear in body creases like the neck, armpits, or groin. These patches sometimes also show up on the hands, elbows, or knees. The darkening is a direct sign of insulin resistance, meaning your body is producing extra insulin to try to manage blood sugar that’s creeping too high. It’s particularly common in people with obesity and can indicate prediabetes or type 2 diabetes.
Skin tags, dry skin, and itching that doesn’t resolve with moisturizer are other dermatological signals worth noting.
What the Numbers Actually Mean
Symptoms give you clues, but blood tests give you answers. Two tests are most commonly used, and it helps to know what the results mean before you get them.
A fasting blood sugar test measures glucose after you haven’t eaten for at least 8 hours. A reading below 100 mg/dL is normal. Between 100 and 125 mg/dL falls in the prediabetes range. At 126 mg/dL or higher on two separate tests, the result indicates diabetes.
An A1C test works differently. Instead of capturing a single moment, it reflects your average blood sugar over the past two to three months. A normal A1C is below 5.7%. Between 5.7% and 6.4% indicates prediabetes, and the higher you are within that range, the greater your risk of progressing to diabetes. An A1C of 6.5% or above means diabetes.
The A1C is useful because it isn’t affected by what you ate yesterday or whether you fasted properly. It paints a broader picture.
Testing at Home
If you already have a glucose meter or are considering one, home testing can help you spot patterns your body’s symptoms might not reveal. The process involves pricking your fingertip, placing a drop of blood on a test strip, and reading the result on a small handheld device.
A few things affect accuracy. Wash your hands with warm, soapy water before testing, because residue from food or lotion on your fingers can skew readings. If your hands are cold, warm them up first since restricted blood flow to your fingertips makes it harder to get an adequate blood sample. Squeeze gently from the base of your finger rather than right at the tip. Store test strips in their sealed container away from moisture and extreme temperatures, as damaged strips give unreliable results.
Continuous glucose monitors are another option. These small sensors sit just under the skin and track glucose levels throughout the day, giving you a running picture rather than isolated snapshots. They’re especially useful for catching overnight highs or post-meal spikes you’d otherwise miss.
When High Blood Sugar Becomes an Emergency
Most of the time, high blood sugar is a slow-building problem. But it can escalate into a dangerous condition called diabetic ketoacidosis, which happens when your body starts breaking down fat so aggressively that it floods your blood with acids called ketones.
The warning signs are distinct: extreme thirst, nausea or vomiting, belly pain, shortness of breath, fruity-smelling breath, weakness, and confusion. A blood sugar reading above 300 mg/dL on more than one test is a red flag. If you have ketones in your urine (detectable with over-the-counter urine strips) and can’t reach a healthcare professional, that’s a reason to seek emergency care. Diabetic ketoacidosis is most common in type 1 diabetes but can occur in type 2 as well, particularly during illness or infection.
The fruity breath is a particularly telling sign. It comes from acetone, a byproduct of the rapid fat breakdown, and it’s different from any food or drink odor. If someone around you notices it, take it seriously even if you feel only mildly unwell.