A blood sugar reading below 70 mg/dL is considered low. This threshold applies whether you have diabetes or not, and it’s the number used by the CDC and most clinical guidelines as the cutoff for hypoglycemia. Below 54 mg/dL is classified as severely low and requires immediate help from another person. Understanding where these lines fall, what symptoms to expect at each stage, and how to respond can prevent a minor dip from becoming a medical emergency.
The Key Numbers to Know
Blood sugar exists on a spectrum, and different levels of low carry different risks. Here’s how the ranges break down:
- Below 70 mg/dL: Officially low. You’ll likely feel early warning symptoms and can usually treat it yourself.
- Below 54 mg/dL: Severely low. Cognitive function starts to decline noticeably, and you may need someone else to help you.
- Below 40 mg/dL: Dangerously low. Seizures, loss of consciousness, and medical emergencies become real possibilities.
For pregnant women with type 1 or type 2 diabetes, the American College of Obstetricians and Gynecologists uses a slightly more cautious threshold of 60 mg/dL as the point to take action. Pregnancy increases the risk of low blood sugar episodes even with careful monitoring, so the lower trigger reflects that added vulnerability.
If you’re outside the U.S. and your meter reads in mmol/L, 70 mg/dL converts to about 3.9 mmol/L, and 54 mg/dL is about 3.0 mmol/L.
What Low Blood Sugar Feels Like
Your body has a built-in alarm system for falling blood sugar. As levels drop below 70 mg/dL, your adrenal glands release stress hormones to push glucose back into your bloodstream. That hormonal surge is what creates the first wave of symptoms: shaking or trembling, a racing heart, sudden intense hunger, sweating, dizziness, and anxiety or irritability. Some people also notice tingling in their lips, tongue, or cheeks, or see the color drain from their skin.
If blood sugar keeps falling, the brain starts running short on fuel. This produces a different, more alarming set of symptoms: confusion, blurred or double vision, slurred speech, poor coordination, and difficulty concentrating. At the severe end, seizures and loss of consciousness can occur. The shift from “I feel shaky” to “I can’t think straight” can happen within minutes, which is why acting on early symptoms matters so much.
Low Blood Sugar While Sleeping
Nocturnal hypoglycemia is particularly tricky because you’re not awake to notice the early warnings. Blood sugar can drop below 70 mg/dL during sleep, and the signs are easy to miss or misinterpret. A bed partner might notice restless or irritable sleep, sweating through pajamas or sheets, sudden changes in breathing, trembling, or a racing heartbeat. Nightmares are another common clue. You might wake up feeling exhausted, confused, or disoriented without understanding why.
Several factors raise the risk of overnight drops: skipping dinner, exercising close to bedtime, drinking alcohol in the evening, and certain types of insulin that peak six to eight hours after injection. If you wake up with unexplained headaches or fatigue regularly, overnight lows are worth investigating with a continuous glucose monitor or a middle-of-the-night finger stick.
Common Causes of Low Readings
For people with diabetes, the most frequent cause is a mismatch between insulin (or other glucose-lowering medication) and food intake. Taking your usual dose but eating less than normal, delaying a meal, or exercising more than expected can all tip the balance. Alcohol makes things worse because it blocks your liver’s ability to release stored glucose.
People without diabetes can also experience low blood sugar, though it’s less common. Reactive hypoglycemia causes blood sugar to drop within four hours after a meal, typically because the body overshoots its insulin response to a large carbohydrate load. Other causes in non-diabetics include certain medications, excessive alcohol consumption, liver or kidney disease, and rarely, insulin-producing tumors.
Doctors confirm hypoglycemia in people without diabetes using a three-part test called Whipple’s triad: symptoms consistent with low blood sugar, a low glucose reading from a laboratory blood draw (not just a home meter) taken while symptoms are present, and resolution of those symptoms once blood sugar is raised. All three criteria need to be met because blood sugar meters have a margin of error, and some people show low readings on a meter without actually being hypoglycemic.
How to Treat a Low Reading
The standard approach is called the 15-15 rule. When your blood sugar is below 70 mg/dL, eat or drink 15 grams of fast-acting carbohydrates, then wait 15 minutes and recheck. If you’re still below 70, repeat the process. Keep going until your reading is back in your target range, then follow up with a balanced snack or small meal that includes protein and carbohydrates to keep levels stable.
Good options for that initial 15 grams include:
- 4 ounces (half a cup) of juice or regular soda
- 1 tablespoon of sugar, honey, or syrup
- 3 to 4 glucose tablets
- 1 tube of glucose gel
- A small handful of hard candies, jellybeans, or gumdrops (check the label for the right amount)
Young children, especially infants and toddlers, typically need less than 15 grams. Your pediatrician can give you a specific amount based on your child’s age and weight.
For severe episodes where someone has lost consciousness or is having a seizure, do not put food or liquid in their mouth. They could choke. This is when injectable or nasal glucagon is used. Glucagon is a hormone that signals the liver to release stored glucose rapidly. If you take insulin, having a glucagon kit accessible to the people around you (family, coworkers, teachers) is a basic safety measure. After using it, call for medical help immediately.
Why Readings Can Vary Between Meters
Home glucose meters are allowed a margin of error of about 15% to 20% under FDA standards. That means if your actual blood sugar is 70 mg/dL, your meter could show anywhere from roughly 56 to 84 mg/dL and still be considered “accurate.” This matters most at lower ranges, where a small error can be the difference between a normal reading and one that looks dangerously low.
Factors that affect accuracy include temperature extremes, expired test strips, dirty or wet fingers, and altitude. If a reading doesn’t match how you feel, wash your hands, use a fresh strip, and test again. Continuous glucose monitors have their own lag time of about 5 to 15 minutes because they measure glucose in the fluid between cells rather than directly in the blood, so during a fast drop, your actual blood sugar may already be lower than what the screen shows.
Patterns Worth Paying Attention To
A single low reading after an unusually long gap between meals is generally not a cause for concern. Patterns are what matter. If you’re seeing readings below 70 mg/dL multiple times a week, or if you’re experiencing symptoms of low blood sugar regularly, your medication, meal timing, or activity level likely needs adjustment. Keeping a log of when lows happen, what you ate, when you last exercised, and what medication you took gives your doctor useful data to work with.
Repeated lows also create a condition called hypoglycemia unawareness, where your body stops producing the early warning symptoms (shaking, sweating, racing heart) because it has adapted to frequent drops. This is dangerous because you lose your built-in alarm. The fix is usually a period of several weeks where blood sugar is kept strictly above the low threshold, which retrains your body to recognize and respond to drops again.