Yes. Fever, illness, and infection can raise glucose because the body releases stress hormones and becomes less responsive to insulin.
In many people, an infection pushes blood sugar up. That can happen with a cold, the flu, a chest infection, a urinary tract infection, an infected tooth, or a skin wound that has turned angry and sore. The rise may be mild. It may also be sharp. The swing is often bigger in people who already have diabetes.
The reason is not just “being sick.” When your body is fighting germs, it releases stress hormones. Those hormones tell the liver to send more glucose into the blood. At the same time, your cells may not respond to insulin as well as they usually do. Put those two changes together, and readings can climb fast.
That is why sick-day planning matters. If your numbers run high for too long, you can become dehydrated, worn down, and more likely to need urgent care. If you use insulin, high readings during an infection can also go along with ketones. This article walks through what happens, what to watch, and what to do next.
Does Infection Increase Blood Sugar? Why It Happens
Yes, infection can increase blood sugar, and the rise is not random. Your body treats illness as a stress event. In response, it releases hormones such as cortisol and adrenaline. These hormones are useful in a fight-or-flight setting, but they also push glucose into the bloodstream.
At the same time, insulin may not work as cleanly as it does on a normal day. That means glucose lingers in the blood longer. If you already have diabetes, that extra glucose can stack up quickly. If you do not have diabetes, a bad infection can still raise blood sugar for a short stretch, though the body often brings it back down once the illness passes.
There is another layer. People often move less when they are ill. They may sleep more, drink less water, or miss meals. Some over-the-counter products can contain sugar, and some prescription drugs, such as steroids, can send readings even higher. So the infection itself matters, but so do the knock-on effects around it.
Who Tends To See The Biggest Rise
People With Diabetes
If you have type 1 or type 2 diabetes, an infection can turn a steady routine into a rough day within hours. A reading that usually stays in range can move well above it, even if you are eating less than usual. That surprises many people the first time it happens. They assume fewer meals should mean lower glucose. During illness, the body does not always play by that rule.
Type 1 diabetes needs extra care here. When insulin is too low during sickness, the body may start making ketones. That can move into diabetic ketoacidosis, which is an emergency. Type 2 diabetes can also become dangerous during illness, especially with dehydration and long stretches of high glucose.
People Without Known Diabetes
A serious infection can raise blood sugar in people who have never been told they have diabetes. That rise may settle after recovery. But if the numbers are high enough, or if the illness seems to “unmask” a hidden problem, follow-up testing may be needed after the infection is gone.
This does not mean every fever points to diabetes. It means illness can reveal how well the body handles glucose under strain. If someone has repeated high readings during or after infection, a clinician may want to check further.
What A Rising Blood Sugar Can Feel Like
Some people feel nothing at first. Others notice thirst, dry mouth, tiredness, blurred vision, or a need to urinate more often. During an infection, those signs can blend into the illness itself, which makes them easy to miss. That is one reason home checks matter more than guesswork when you are unwell.
You may also notice that a reading stays high longer than usual after meals. Or it may start high in the morning and stay that way through the day. If vomiting, belly pain, or deep tiredness show up on top of high glucose, do not shrug that off. Those can be red-flag signs, mainly in people who use insulin.
What Usually Happens During Sick Days
Not every infection causes the same pattern, but a few sick-day trends show up again and again. The table below gives a plain view of what often changes and what action fits the moment.
| Situation | What Often Happens | Practical Response |
|---|---|---|
| Fever or active infection | Stress hormones push glucose higher | Check more often and write the numbers down |
| Eating less than usual | Glucose may still stay high, but some people dip low | Keep checking and use your sick-day meal plan |
| Vomiting or diarrhea | Fluid loss can drive readings up and make you weak | Sip fluids often and seek care if you cannot keep fluids down |
| Missed diabetes medicine | Glucose can climb fast | Do not skip medicine unless your care plan says to |
| Steroid treatment | Readings may run much higher than usual | Ask for a clear dose-adjustment plan |
| Type 1 diabetes with high glucose | Ketones may develop | Check ketones and act on sick-day rules right away |
| Type 2 diabetes with dehydration | High glucose may become harder to bring down | Push fluids and seek care if numbers stay high |
| Recovery after infection | Readings often settle over days | Keep checking until the pattern feels normal again |
What To Do When You Are Sick
Check More Often Than Usual
Illness is not the time to “wait and see” for half a day. If you have diabetes, more frequent checks give you a real picture of what the infection is doing. The CDC’s sick-day advice says to test blood sugar every four hours and keep track of the results. That one step can stop a rough day from turning into a dangerous one.
Do Not Stop Diabetes Medicine On Your Own
Many people assume they should skip medicine if they are not eating much. That can backfire. During infection, your body may need the same medicine or even more, not less. Insulin should not be stopped just because you feel sick to your stomach or off your food. If you have a written sick-day plan from your care team, use it. If you do not, ask for one before the next illness hits.
Drink Fluids Early
High blood sugar pulls water out of the body through extra urination. Fever, sweating, vomiting, and diarrhea can add to that loss. Small, frequent sips often work better than trying to gulp a large glass at once. Water is a good first choice. If you cannot eat, you may also need fluids that give some carbohydrate, based on your readings and your usual treatment plan.
Know When To Check Ketones
If you have diabetes and your readings are high while you are ill, ketones matter. The CDC’s guidance on diabetic ketoacidosis says to check for ketones when you are sick or when blood sugar is 250 mg/dL or higher. Ketones with rising glucose, nausea, or belly pain are not a “sleep it off” issue.
When An Infection Can Turn Dangerous
Most infections raise blood sugar in a way that can be managed at home with more checks, fluids, and a clear medicine plan. But there are times when the pattern points to urgent trouble. The biggest danger signs are dehydration, ketones, vomiting that does not stop, heavy sleepiness, confusion, and trouble breathing.
In type 1 diabetes, the major worry is diabetic ketoacidosis. In type 2 diabetes, severe dehydration with very high glucose can also become an emergency. These are not rare textbook events. They are the reason sick-day rules exist in the first place.
The American Diabetes Association’s sick-day page also points people to call for medical advice if vomiting or diarrhea keeps going, or if a fever stays above 101°F for a full day. A bad infection can move quickly. Early care is a lot easier than rescue care.
| Warning Sign | Why It Matters | Next Step |
|---|---|---|
| Blood sugar stays above your usual range for hours | The illness may be overpowering your usual plan | Call your clinic for sick-day advice |
| Ketones are present | This can lead to diabetic ketoacidosis | Get medical advice the same day |
| You cannot keep fluids down | Dehydration can build fast | Seek urgent care |
| Deep tiredness, confusion, or hard breathing | These can point to a medical emergency | Go to urgent care or the ER now |
Food, Drinks, And Rest During Illness
If you can eat, stick with plain foods that sit well and are easy to count. If your stomach is off, try small portions instead of full meals. Soup, toast, yogurt, crackers, rice, or applesauce may be easier to manage than greasy or heavy food. The goal is not a perfect menu. The goal is steady intake, enough fluid, and no long stretch where you stop paying attention to glucose because you feel miserable.
Rest matters too, but total inactivity can push numbers up in some people. You do not need a workout while you have a fever. You do need to keep an eye on the pattern and avoid going all day without checking because you stayed in bed.
When To Call A Clinician
Call sooner rather than later if blood sugar keeps climbing, ketones appear, or you are not sure how to adjust medicine. Also call if you have a high fever that is hanging on, signs of a urinary infection, a spreading skin wound, or a cough with shortness of breath. Those are not just glucose problems. They may point to an infection that needs treatment on its own.
If you do not have diabetes but notice repeated high readings during an infection, it is smart to ask for follow-up testing after recovery. One sick week does not answer every question, but it can flag a problem worth checking.
Daily Habits That Lower Sick-Day Trouble
The best sick-day fix starts before you get sick. Keep your meter, strips, ketone supplies, medicines, and simple foods in one place. Write down your usual doses and the phone number you would call if numbers swing out of range. If you use insulin, ask for clear steps for fever days, stomach-bug days, and steroid days. Those three settings can play out quite differently.
Also pay attention to the infections that start small and then drag blood sugar higher for days, such as gum problems, foot wounds, and urinary symptoms. Catching the infection early often makes the glucose rise easier to manage too.
The Main Takeaway
Infection often raises blood sugar because illness changes the way your body handles glucose and insulin. That rise can be mild, or it can be steep. More checks, enough fluid, and a clear sick-day plan make a big difference. If readings stay high, ketones show up, or you cannot keep fluids down, get medical care quickly. Sick days are manageable, but they should never be brushed aside.
References & Sources
- Centers for Disease Control and Prevention (CDC).“Managing Sick Days.”Explains sick-day steps for people with diabetes, including checking blood sugar every four hours, staying hydrated, and watching for fever.
- Centers for Disease Control and Prevention (CDC).“Diabetic Ketoacidosis.”Lists warning signs of DKA and says people with diabetes should check blood sugar and ketones during illness or when readings are 250 mg/dL or higher.
- American Diabetes Association (ADA).“Diabetes and Planning for Sick Days.”Gives sick-day guidance on glucose checks, fluids, ketone checks, and when to call a doctor during fever, vomiting, or diarrhea.