For most people without diabetes, blood sugar is considered low when it drops below 55 mg/dL (3.1 mmol/L). For people with diabetes, the threshold is slightly higher: readings below 70 mg/dL are typically flagged as low. Below 54 mg/dL is classified as severe low blood sugar, which can cause fainting, confusion, and seizures.
How Low Blood Sugar Compares to Normal
A normal fasting blood sugar level falls below 100 mg/dL. That means there’s a wide comfortable zone between “normal” and “low.” Your body keeps blood sugar remarkably stable throughout the day, and most healthy people will never dip below 70 mg/dL even between meals or overnight.
The gap between the diabetes threshold and the non-diabetes threshold exists because people taking insulin or certain diabetes medications are more vulnerable to drops. Their bodies may not mount the usual hormonal response that prevents blood sugar from falling too far. That’s why clinical guidelines set the alarm at 70 mg/dL for anyone managing diabetes, giving more room to catch a drop before it becomes dangerous.
Key Numbers at a Glance
- Below 70 mg/dL: Considered low for people with diabetes. Early warning symptoms like shakiness and sweating often start here.
- Below 55 mg/dL: Considered low for people without diabetes. Symptoms are usually noticeable at this point.
- Below 54 mg/dL: Classified as severe low blood sugar regardless of diabetes status. Risk of fainting, seizures, and loss of consciousness increases significantly.
What Low Blood Sugar Feels Like
Early symptoms are your body’s alarm system kicking in. When blood sugar starts dropping, you release stress hormones that cause sweating, a rapid heartbeat, shakiness, and hunger. You might feel anxious or irritable for no clear reason. These warning signs are your cue to eat something.
As blood sugar falls further, the brain starts running short on fuel. That’s when symptoms shift from uncomfortable to concerning: difficulty walking, blurred vision, confusion, slurred speech, and strange behavior that other people may notice before you do. Below 54 mg/dL, you can lose consciousness or have a seizure. At that point, you often can’t treat yourself and need someone else to help.
Some people, particularly those who have had diabetes for many years, lose the ability to feel those early warning signs. This condition, called hypoglycemia unawareness, means blood sugar can drop dangerously low without the usual sweating or shakiness to signal a problem.
Low Blood Sugar During Pregnancy
Pregnant women are generally advised to keep blood sugar between 60 and 120 mg/dL. Readings below 60 mg/dL during pregnancy call for immediate treatment with about 15 grams of fast-acting carbohydrates or three glucose tablets. If blood sugar drops below 40 mg/dL, the recommendation is to drink a full cup (8 ounces) of juice to bring levels up quickly.
Pregnancy changes how the body processes glucose, and hormonal shifts can make blood sugar less predictable. Women managing gestational diabetes or pre-existing diabetes during pregnancy are at higher risk for lows, especially if they’re adjusting insulin doses.
How to Treat a Low
The standard approach is called the 15-15 rule: eat or drink 15 grams of fast-acting carbohydrates, wait 15 minutes, then check your blood sugar again. If it’s still low, repeat. Fifteen grams of carbohydrates looks like about four glucose tablets, half a cup of juice or regular soda, or a tablespoon of honey.
The goal is to choose something your body absorbs quickly. A candy bar or a slice of pizza won’t work well because the fat slows digestion. You want pure sugar that hits your bloodstream fast. Once your blood sugar stabilizes, eating a small meal or snack with protein and complex carbohydrates helps prevent another drop.
For severe episodes where someone has lost consciousness or can’t swallow safely, bystanders should not try to put food or liquid in the person’s mouth. Injectable or nasal glucagon kits are designed for exactly this situation, and anyone at risk for severe lows should have one accessible and make sure the people around them know how to use it.
Common Causes
In people with diabetes, the most frequent triggers are taking too much insulin, skipping or delaying meals, exercising more than usual, and drinking alcohol without eating. These all create a mismatch between the amount of glucose available and the amount of insulin in the bloodstream.
In people without diabetes, low blood sugar is less common but can happen. Prolonged fasting, heavy alcohol consumption, certain medications, and some medical conditions affecting the liver, kidneys, or hormone-producing glands can all drive blood sugar below normal. Reactive hypoglycemia, where blood sugar drops a few hours after eating (especially after a high-carbohydrate meal), is another pattern some people experience. If you’re getting repeated low readings without an obvious explanation, that’s worth investigating with a healthcare provider, since it can occasionally signal an underlying condition like an insulin-producing tumor or adrenal insufficiency.