Have you ever noticed that your blood sugar levels rise when you have a fever, cold, cough, urinary tract infection, or another illness? Even if you are eating less than usual, your glucose readings may suddenly become higher than normal.
An infection can increase blood sugar levels because the body releases stress hormones to fight the illness. These hormones can increase glucose production by the liver and make insulin less effective.
This is particularly important for people living with diabetes because their bodies may have difficulty controlling the additional glucose released during an infection. In some cases, blood sugar can remain high until the illness improves.
At Dr. Rajender’s Lifestyle Clinic, understanding the factors that influence blood glucose is an important part of diabetes management. Let us explore why infections affect blood sugar, which warning signs to watch for, and how to manage glucose safely during illness.
1. Why Does Blood Sugar Increase During an Infection?
When bacteria, viruses, or other harmful microorganisms enter the body, the immune system begins working to fight the infection.
During this process, the body activates its natural stress response. Hormones such as cortisol, adrenaline, and glucagon help make additional energy available to the body’s tissues.
One source of this energy is glucose.
The liver releases more glucose into the bloodstream, while hormonal changes can reduce the body’s sensitivity to insulin. As a result, glucose may accumulate in the blood rather than entering cells efficiently.
This is known as infection-related hyperglycemia, which means high blood sugar associated with an illness.
People with diabetes are especially vulnerable because they may not produce enough insulin or may already have insulin resistance.
2. How Do Stress Hormones Affect Blood Sugar During an Infection?
Several hormones contribute to changes in blood glucose during illness.
Cortisol
Cortisol helps the body respond to physical stress. During an infection, increased cortisol activity can stimulate glucose production by the liver and reduce insulin sensitivity.
This can cause blood sugar to rise even if your food intake has not increased.
Adrenaline
Adrenaline helps the body respond to demanding situations. During an illness, it can stimulate the release of glucose stored in the liver.
This response can contribute to sudden or temporary increases in blood glucose.
Glucagon
Glucagon is a hormone that signals the liver to release glucose when the body needs energy. During illness, its effects can contribute to higher blood sugar levels.
Together, these hormonal changes help the body respond to illness, but they can make glucose control more difficult in people with diabetes.
3. Which Infections Can Cause High Blood Sugar?
Many types of infections can affect blood glucose levels. The effect depends on the severity of the infection, the person’s health, and whether they have diabetes or another condition affecting glucose regulation.
Respiratory Infections
Common colds, influenza, bronchitis, and pneumonia can cause blood sugar levels to rise. Fever, inflammation, reduced activity, and stress hormones may all contribute.
Urinary Tract Infections
Urinary tract infections can cause glucose levels to become elevated, particularly in people with diabetes. Symptoms may include burning during urination, frequent urination, lower abdominal discomfort, or fever.
However, frequent urination can also occur because blood sugar is high, so symptoms should be assessed carefully.
Skin and Soft Tissue Infections
Skin infections, infected wounds, and foot ulcers may affect blood glucose. In people with diabetes, high glucose can also impair aspects of immune function and wound healing, creating a cycle in which infection and poor glucose control make each other harder to manage.
Gastrointestinal Infections
Vomiting, diarrhoea, and other gastrointestinal infections can disrupt food intake and fluid balance. Blood sugar may rise due to the body’s stress response, but it can also fall if a person is eating very little while continuing certain diabetes medications.
Dental and Gum Infections
Gum disease, dental abscesses, and other oral infections can cause inflammation and contribute to elevated glucose levels. Persistent oral infections should be assessed by a dental professional.
4. Why Can Blood Sugar Rise Even When You Eat Less During an Infection?
Many people assume that eating less should automatically lower blood sugar. However, glucose levels are influenced by more than food alone.
During an infection, the liver can release stored glucose and produce additional glucose to meet the body’s energy needs.
At the same time, stress hormones can make insulin less effective. This means blood sugar may increase even when appetite is reduced.
For people taking insulin or certain diabetes medications, eating less than usual can also increase the risk of low blood sugar.
The key point is that illness can cause both high and low blood sugar. Monitoring glucose and following an appropriate sick-day plan are important, especially when food intake changes.
5. What Are the Symptoms of High Blood Sugar During an Infection?
High blood sugar may cause symptoms such as:
- Increased thirst
- Frequent urination
- Dry mouth
- Unusual tiredness
- Blurred vision
- Headache
- Difficulty concentrating
An infection may also cause fever, chills, body aches, cough, painful urination, or other symptoms depending on its location.
These symptoms can overlap. For example, fatigue may be caused by the infection, high blood sugar, dehydration, or a combination of factors.
If you have diabetes and become ill, check your blood glucose more frequently according to your healthcare professional’s instructions. Do not rely on symptoms alone to determine whether your glucose is high or low.
6. Can an Infection Cause Very High Blood Sugar?
Yes. A significant infection can cause substantial increases in blood glucose, especially in people with diabetes.
Very high glucose levels can contribute to dehydration because the kidneys remove excess glucose through urine, increasing fluid loss.
In some people, illness can trigger serious complications such as diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemic state (HHS).
Warning Signs That Need Urgent Medical Attention
Seek urgent medical care if you experience:
- Repeated vomiting or an inability to keep fluids down
- Abdominal pain
- Rapid or deep breathing
- Fruity-smelling breath
- Confusion or unusual drowsiness
- Severe weakness or signs of significant dehydration
- Very high blood sugar that remains elevated despite following your prescribed sick-day plan
DKA can sometimes occur even when glucose is not extremely high, particularly in people taking SGLT2 inhibitor medicines. If you take one of these medicines and develop symptoms suggestive of DKA, seek urgent medical assessment even if your glucose reading is not very high.
If you use insulin and have been instructed to check ketones during illness or high glucose readings, follow that guidance. Do not delay emergency care while waiting for another reading.
7. How Should You Manage Blood Sugar During an Infection?
Managing diabetes during illness requires attention to glucose levels, hydration, food intake, medications, and infection symptoms.
Monitor Blood Sugar More Frequently
Check your blood glucose according to your clinician’s sick-day instructions. Some people with diabetes may need to check every few hours while ill, depending on their treatment and the severity of the illness.
Record your readings and note symptoms, food intake, and medication use. This information can help your healthcare professional decide whether your treatment needs adjustment.
Stay Hydrated
Drink water regularly, unless your healthcare professional has advised you to restrict fluids because of a heart or kidney condition.
Fever, vomiting, diarrhoea, and frequent urination can all increase fluid loss. Dehydration can make glucose management more difficult.
If you cannot keep fluids down, seek prompt medical advice.
Continue Eating What You Can Tolerate
Try to maintain suitable nutrition during illness. If you cannot eat your usual meals, ask your healthcare professional for advice on alternatives that fit your treatment plan.
Do not force yourself to eat large meals, but do not assume that eating nothing is the safest way to lower glucose.
If you take insulin or medicines that can cause hypoglycemia, reduced food intake requires particular care.
Follow Your Prescribed Medication Plan
Do not stop insulin on your own because you are eating less or feeling unwell. Some people need insulin even when they cannot eat normally.
However, certain medicines may require temporary changes during dehydration, vomiting, diarrhoea, or severe illness. For example, SGLT2 inhibitors and metformin may need to be withheld in specific circumstances under a clinician’s sick-day guidance.
Contact your healthcare professional for medicine-specific instructions. Do not start, stop, or change doses without appropriate advice.
Treat the Infection Appropriately
The underlying infection needs proper assessment and treatment. Depending on the cause, treatment may involve supportive care, prescription medication, or urgent medical intervention.
Antibiotics treat bacterial infections, not viral infections, and should only be used when clinically indicated. Avoid self-medicating with leftover antibiotics.
Rest and Allow Time for Recovery
Adequate rest supports recovery. Avoid strenuous exercise if you have a fever, feel significantly unwell, are dehydrated, or have ketones.
Once you recover, review your glucose readings with your healthcare professional if they remain outside your usual target range.
8. How Long Does Blood Sugar Stay High After an Infection?
The duration varies depending on the type and severity of infection, the person’s glucose control, medications, hydration, and recovery.
For some people, glucose levels improve as the infection resolves. For others, blood sugar may remain elevated for several days or longer, particularly if the illness is severe or diabetes treatment needs adjustment.
If your glucose readings remain higher than your target after the infection improves, contact your healthcare professional. They may need to assess medication requirements, possible complications, or other causes of persistent hyperglycemia.
An HbA1c test may help evaluate longer-term glucose control, but it does not replace immediate glucose monitoring during an acute illness.
9. How Can People With Diabetes Reduce Infection-Related Risks?
Although not all infections can be prevented, several steps may help reduce risks and support recovery.
- Maintain glucose control: Follow your individual treatment plan and attend regular reviews.
- Practise good hygiene: Wash your hands regularly and follow appropriate food safety practices.
- Keep vaccinations up to date: Ask your healthcare professional which vaccines are recommended for your age and medical conditions.
- Care for your feet: Check for cuts, blisters, redness, swelling, or wounds, especially if you have reduced sensation.
- Look after oral health: Brush regularly and attend dental check-ups.
- Avoid smoking: Smoking can adversely affect vascular health and healing.
- Seek care early: Do not ignore persistent fever, worsening symptoms, or signs of infection.
People with diabetes may benefit from having a written sick-day plan that explains when to check glucose and ketones, how to manage medicines, when to contact their clinician, and when to seek emergency care.
10. When Should You Consult a Diabetes Specialist?
Contact your healthcare professional if:
- Your blood sugar is repeatedly above your prescribed target during illness.
- You have a fever or infection that is worsening or not improving.
- You have repeated vomiting or diarrhoea.
- You are unable to eat or drink normally.
- You are unsure whether to continue a particular diabetes medicine.
- Your glucose readings remain high after the infection has improved.
Seek emergency care for symptoms of DKA, severe dehydration, confusion, breathing difficulties, or other signs of serious illness.
Early assessment can help identify the cause of elevated glucose and reduce the risk of complications.
How Dr. Rajender’s Lifestyle Clinic Can Help
Dr. Rajender’s Lifestyle Clinic in Banjara Hills, Hyderabad, focuses on evidence-based lifestyle and medical support for people managing Type 2 diabetes and other metabolic conditions.
Dr. Rajender Ramagiri, Founder and Lead Physician, combines medical guidance with nutrition and sustainable lifestyle changes to support long-term metabolic health.
Depending on individual needs, diabetes care may include:
- Personalised nutrition guidance
- Blood glucose monitoring and review
- Support with daily lifestyle habits
- Medical assessment and treatment guidance
- Follow-up to review glucose patterns and progress
If your blood sugar rises whenever you become ill, a healthcare professional can help you understand your glucose patterns and prepare an appropriate sick-day management plan.
For diabetes care and personalised lifestyle guidance, contact Dr. Rajender’s Lifestyle Clinic in Banjara Hills, Hyderabad.
Frequently Asked Questions (FAQs)
1. Can a common cold increase blood sugar?
Yes. Even a mild respiratory infection can activate stress hormones and affect insulin sensitivity. The effect varies from person to person, but people with diabetes may notice higher readings during illness.
2. Why does blood sugar increase during a fever?
Fever often occurs as part of the body’s response to infection. Stress hormones and inflammatory processes can increase glucose production and reduce insulin sensitivity, causing blood sugar to rise.
3. Can an infection cause high blood sugar without diabetes?
Yes. Significant infections can cause temporary hyperglycemia in people without diabetes. If high readings persist after recovery, medical evaluation is important to investigate diabetes or other causes.
4. Should I stop diabetes medication when I have an infection?
Do not stop or adjust your medication without medical guidance. Some medicines may need temporary changes during certain illnesses, while insulin may still be essential even when you eat less. Follow a personalised sick-day plan.
5. Can high blood sugar make an infection worse?
Diabetes and elevated glucose can impair some immune responses and delay wound healing. This may make certain infections harder to manage, although the relationship depends on the infection and the person’s overall health.
6. What should I eat when blood sugar is high during an infection?
Choose foods and fluids appropriate for your symptoms and treatment plan. If possible, maintain balanced nutrition and hydration. If vomiting, diarrhoea, or poor appetite makes eating difficult, ask your healthcare professional for advice rather than fasting or making major dietary changes.
7. When should I worry about high blood sugar during illness?
Seek urgent medical care if high glucose occurs with vomiting, abdominal pain, rapid or deep breathing, confusion, severe dehydration, or unusual drowsiness. Contact your clinician if readings remain above your target or you are unsure how to manage medication.
8. Does blood sugar return to normal after an infection?
It often improves as the illness resolves, but not always immediately. Persistent elevation may require medical assessment and a review of your diabetes management plan.
Conclusion
Blood sugar often increases during an infection because the body releases stress hormones and changes how it uses and produces glucose. Fever, inflammation, dehydration, reduced insulin sensitivity, and changes in daily routines can all contribute.
For people with diabetes, monitoring glucose, staying appropriately hydrated, following a personalised sick-day plan, and treating the underlying infection are important. Both high and low blood sugar can occur during illness, so medication and food intake need careful management.
If your glucose readings remain high during an infection or you experience concerning symptoms, seek medical advice promptly.
Dr. Rajender’s Lifestyle Clinic, Banjara Hills, Hyderabad, provides diabetes care and lifestyle guidance to help individuals work toward better long-term metabolic health.
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