What causes low-grade fever in the elderly?

Oct 23, 2025 3 min read •

Geriatrics senior care Healthy Aging

Approximately 20–30% of older adults with serious infections may not exhibit a high-grade fever, which makes recognizing less pronounced signs, such as a low-grade fever, crucial. Understanding what causes low-grade fever in the elderly is a critical aspect of effective senior care, as it can be the only sign of an underlying health issue. This guide explores the various causes, from common infections to more complex health conditions.

Quick Summary

Low-grade fever in the elderly can be caused by infections like UTIs and pneumonia, chronic inflammatory conditions such as rheumatoid arthritis, or side effects from medications. Because an aging immune system may not mount a robust febrile response, this subtle temperature rise is a significant warning sign that requires careful attention and often warrants medical evaluation. It can signal a more serious underlying issue than it would in a younger person.

Key Points

Atypical Presentation: Low-grade fevers in the elderly are significant because their immune system may not produce a high-grade fever even with a serious infection.
Baseline Temperature Matters: An older person's normal body temperature is often lower, so a slight elevation could be a genuine fever.
Infections are Common: Hidden infections, particularly UTIs, respiratory infections, and skin infections, are frequent causes.
Medication Side Effects: Drug-induced fever, especially in seniors on multiple prescriptions, is a possibility and should be investigated.
Chronic Illnesses: Autoimmune disorders, cancers, and blood clots can also cause persistent low-grade fevers.
Behavioral Changes are Key: Caregivers should look for signs like confusion, weakness, or agitation, as these can accompany a fever in seniors.
When to Call a Doctor: Seek medical attention for any unexplained fever, or if the fever is accompanied by severe or persistent symptoms.

The Significance of Atypical Fevers in Seniors

An elderly person's normal body temperature is typically lower than that of younger adults. A low-grade fever in a senior can be more significant than in a younger person due to a subdued immune response that may not produce a high fever even with a serious infection. An oral temperature above 99°F or a rise of 2°F above their baseline can be concerning. Atypical symptoms like confusion or weakness may be present instead of classic fever signs.

Infectious Causes of Low-Grade Fever

Infections are common causes of low-grade fever in seniors due to their weakened immune systems.

Urinary Tract Infections (UTIs)

UTIs frequently cause low-grade fever in the elderly. Unlike younger individuals, seniors might show confusion, lethargy, or agitation rather than typical urinary symptoms.

Respiratory Infections

Pneumonia, influenza, and bronchitis can lead to a low-grade fever. Look for new cough, shortness of breath, or a general feeling of being unwell.

Skin and Soft Tissue Infections

Cellulitis or infections from bedsores can cause inflammation and low-grade fever. A warm, red, and swollen area of skin with fever needs medical evaluation.

Other Hidden Infections

Dental Abscesses: Untreated dental issues can cause fever.
Endocarditis: An infection of the heart lining or valves can result in a persistent low-grade fever.
Tuberculosis: Can present with a persistent low-grade fever.

Non-Infectious Causes of Low-Grade Fever

Non-infectious factors can also cause low-grade fevers.

Inflammatory and Autoimmune Disorders

Conditions with chronic inflammation can cause persistent low-grade fever.

Rheumatoid Arthritis and Lupus: These autoimmune diseases can cause fever due to inflammation.
Vasculitis: Inflammation of blood vessels, like in giant cell arteritis, is a known cause of fever in older adults.

Medication Side Effects

Drug-induced fever is a possibility, especially for seniors taking multiple medications. It often resolves after stopping the offending drug. Certain antibiotics, heart medications, and anticonvulsants are common culprits.

Malignancy

Some cancers, particularly leukemia and lymphoma, can cause a persistent low-grade fever.

Other Potential Causes

Dehydration: Severe dehydration can lead to overheating and mimic fever symptoms.
Deep Vein Thrombosis (DVT) or Pulmonary Embolism (PE): Blood clots can cause inflammation and a low-grade fever.

Comparison: Infections vs. Chronic Conditions


Feature	Infectious Causes	Chronic/Non-Infectious Causes
Onset	Often acute or subacute.	Often insidious and gradual.
Symptom Profile	May include localized signs.	Often accompanied by systemic symptoms like fatigue or weight loss.
Response to Treatment	Responds to appropriate antibiotics or antivirals.	Requires treating the underlying condition or stopping the medication.
Typical Duration	Tends to resolve within days to a week with treatment.	Can be persistent or recurrent.

Diagnosis and When to Seek Medical Attention

Any unexplained fever in an elderly person warrants medical evaluation. Diagnosis involves a physical exam, medication review, and tests.

What to Tell Your Doctor

Provide baseline temperature, fever duration, other symptoms (even subtle ones), and a list of all medications.

When to Seek Immediate Medical Help

Seek immediate help for a temperature above 100.4°F (38°C) or 2°F above baseline, especially with severe symptoms like difficulty breathing, chest pain, stiff neck, extreme weakness, or new confusion. Also, seek help if a fever lasts more than three days or is recurrent.

Conclusion

In seniors, a low-grade fever is a significant sign that needs attention. Due to changes with age, this subtle temperature rise can indicate serious issues, including infections, autoimmune conditions, or drug reactions. Careful monitoring and prompt medical evaluation are crucial in senior care.

For more information on senior health, a great place to start is the National Institute on Aging (NIA), a leading resource on aging-related research. https://www.nia.nih.gov

Frequently Asked Questions

For an elderly person, a single oral temperature reading over 100°F (37.8°C), repeated readings over 99°F (37.2°C), or an increase of 2°F above their normal baseline temperature can be considered a significant fever.

As people age, their immune system becomes less robust. This can blunt the body's inflammatory response, meaning they may not mount a strong fever response even when fighting a serious viral or bacterial infection.

Yes. UTIs are a very common cause of low-grade fever in seniors. It's important to note that many elderly individuals with a UTI may not have typical symptoms like burning or pain, but rather present with confusion or behavioral changes.

Yes, a drug-induced fever is a known side effect of many medications, including some antibiotics, cardiovascular drugs, and anticonvulsants. The risk can increase in seniors taking multiple medications.

You should seek medical attention for any unexplained fever in a senior, especially if it persists for more than three days, or if it is accompanied by other worrying symptoms like confusion, extreme weakness, or difficulty breathing.

Yes, conditions that cause chronic inflammation, such as autoimmune diseases like rheumatoid arthritis or lupus, can lead to a persistent low-grade fever. Certain cancers can also cause a low fever.

While dehydration doesn't cause a true fever (pyrexia), severe dehydration can cause the body to overheat (hyperthermia) and lead to fever-like symptoms. Dehydration can also be caused by fever due to increased fluid loss.

References

Medical Disclaimer

This content is for informational purposes only and should not replace professional medical advice. Always consult a qualified healthcare provider regarding personal health decisions.