A blood sugar level below 70 mg/dL (3.9 mmol/L) is considered low. This is the threshold where your body may start showing warning signs and where you should take steps to bring your levels back up. A reading below 54 mg/dL (3.0 mmol/L) is considered seriously low and requires immediate action.
These numbers apply whether you have diabetes or not, though the causes, symptoms, and risks look different depending on your situation.
The Key Numbers to Know
The American Diabetes Association uses 70 mg/dL as the clinical alert value for low blood sugar, also called hypoglycemia. At this level, glucose is dropping low enough that your body’s stress hormones kick in and symptoms begin. It doesn’t mean you’re in danger at 70, but it does mean the trend is heading somewhere you don’t want it to go.
Below 54 mg/dL, the situation becomes more urgent. At this level, your brain isn’t getting enough fuel to function normally, and confusion, difficulty speaking, or loss of coordination can set in. If blood sugar continues to fall without treatment, seizures or loss of consciousness are possible.
For people without diabetes, the diagnostic bar is slightly different. Doctors generally look for blood sugar below 60 mg/dL along with symptoms and improvement once sugar levels are restored. This three-part checklist (low reading, matching symptoms, symptom relief after eating) is called the Whipple triad, and it’s the standard for confirming that someone truly has a hypoglycemia problem rather than just a one-off dip.
What Low Blood Sugar Feels Like
The symptoms of low blood sugar come in two waves, driven by different parts of your body’s response. The first set of symptoms comes from your body’s fight-or-flight system reacting to the drop. These include shakiness, sweating, a pounding or fast heartbeat, anxiety, and sudden intense hunger. Most people notice these signs when glucose falls into the 60s or low 70s, though this varies from person to person.
If blood sugar keeps falling, a second set of symptoms appears. These come from your brain running short on its primary fuel. You might feel weak, dizzy, or unusually tired. Concentration becomes difficult. Vision can blur. Some people behave in ways that look like intoxication, slurring words or acting confused, which is why bystanders sometimes misread the situation. In extreme cases, a person can lose consciousness.
Children tend to experience symptoms at slightly higher glucose levels than adults. In healthy children without diabetes, warning signs can appear around 70 mg/dL, while healthy adults may not feel anything until levels dip closer to 58 mg/dL. This means kids may need attention sooner, even if the number on the meter doesn’t look dramatically low.
Why Some People Don’t Feel Symptoms
One of the more dangerous complications of frequent low blood sugar is that the body can stop sounding the alarm. This is called hypoglycemia unawareness. When your blood sugar drops repeatedly, your brain adjusts its threshold for triggering those fight-or-flight warning signs. Instead of feeling shaky at 65 mg/dL, you might feel nothing until you’re already at 45, which is well into dangerous territory.
This is most common in people with type 1 diabetes or those with long-standing type 2 diabetes who use insulin. It creates a vicious cycle: the more lows you have, the less you feel them, and the less you feel them, the more likely you are to have severe episodes. Careful glucose monitoring, especially with continuous glucose monitors that can alert you to drops, is one of the main strategies for breaking this cycle.
Common Causes of Low Blood Sugar
For people with diabetes, the most common trigger is a mismatch between medication and what your body actually needs in the moment. Taking your usual dose of insulin but eating less than normal, exercising more than expected, or mistiming a dose can all send blood sugar lower than intended. It’s not necessarily a mistake. Sometimes routines just don’t line up perfectly with biology.
Alcohol is another well-known trigger. When you drink heavily without eating, your liver gets tied up processing the alcohol and can’t release stored glucose into your bloodstream the way it normally would. This can cause a delayed drop in blood sugar, sometimes hours after drinking, which catches people off guard.
For people without diabetes, low blood sugar is less common but does happen. One recognized form is reactive hypoglycemia, where blood sugar drops a few hours after eating. This is most often seen in people who have had stomach bypass surgery or other procedures that change how the stomach processes food, though it can occasionally occur without any surgical history.
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 below 70 mg/dL, repeat the process. Keep going until your levels return to your target range. Good sources of 15 grams of carbs include four glucose tablets, four ounces of juice, or a tablespoon of sugar or honey.
For young children, especially infants and toddlers, the 15-gram amount is often too much. Smaller portions are appropriate, and a pediatrician can help determine the right amount based on age and size.
The key is using simple sugars that hit your bloodstream quickly. A candy bar or a sandwich with peanut butter contains fat and protein that slow digestion, which means the sugar takes longer to reach your blood. That delay matters when your brain is running low on fuel.
When a Low Becomes an Emergency
Severe hypoglycemia, where a person is too confused or unconscious to eat or drink safely, requires outside help. Trying to put food or liquid into the mouth of someone who can’t swallow properly creates a choking risk. This is where glucagon comes in. Glucagon is a hormone that signals the liver to release stored glucose. It’s available as an emergency kit in both injectable and nasal spray forms, and someone nearby (a family member, coworker, or friend) can administer it.
Studies comparing the two delivery methods found that the nasal spray version was more successfully administered by both trained and untrained users during simulated emergencies. If you’re at risk for severe lows, having glucagon accessible and making sure the people around you know where it is and how to use it can be the difference between a scary moment and a genuinely dangerous one.
What Counts as Low Can Vary by Person
While 70 mg/dL is the widely accepted threshold, your personal “too low” level can shift based on your history. Someone who has been running high blood sugars for months might feel symptoms of a low at 90 or 100 mg/dL, even though that number is technically normal. Their body has adapted to higher levels and interprets the drop as a threat. This doesn’t mean they’re truly hypoglycemic, but the discomfort is real.
On the other end, people with frequent lows may feel perfectly fine at 55 mg/dL because their body has stopped reacting. Neither scenario is ideal. Working with a healthcare provider to establish a personal target range, and adjusting medications or habits to stay within it, helps your body recalibrate its alarm system over time.