Fever in Adults: Common Causes, Symptom Patterns and Safe Self-Care

Fever in adults is common – but it also raises many questions: What temperature counts as a fever? When is a fever dangerous? Which symptom combinations are still normal, and when should you see a doctor or go to the emergency department? This guide summarizes up-to-date medical information to help you interpret typical situations.

What counts as a fever in adults?

In adults, an oral temperature of 38.0 °C (100.4 °F) or higher is generally considered a fever. Normal body temperature ranges roughly from 36.0 to 37.5 °C (96.8–99.5 °F) and varies throughout the day.

Remember: fever itself is not a disease, but a symptom. It usually indicates that the body is fighting a trigger – most often a viral or bacterial infection.

How to measure your temperature correctly

• Oral (under the tongue): common in adults and fairly reliable; avoid measuring right after eating or drinking.
• Axillary (under the arm): easy but less accurate; tends to read about 0.3–0.5 °C lower than oral values.
• Ear or forehead thermometers: convenient but highly technique-dependent.

Try to use the same thermometer and similar times of day so you can better compare temperature trends.

Common causes of fever in adults

Most episodes of fever in adults are caused by infections. Some are mild and self-limiting, others can be serious and require prompt evaluation.

Viral respiratory infections

• Common cold: low-grade fever, cough, runny or stuffy nose, sore throat
• Influenza (flu): sudden high fever, marked headache and body aches, dry cough
• COVID-19: fever, dry cough, fatigue; sometimes loss of smell or taste

Bacterial infections

• Urinary tract infection or kidney infection: fever, burning when passing urine, flank pain
• Pneumonia: fever, cough with or without phlegm, shortness of breath, chest pain
• Sinus infection: fever, facial pain or pressure, blocked nose, headache

Gastrointestinal infections

Fever together with diarrhea, nausea or vomiting often points to a gastrointestinal infection. The main risk is dehydration.

Non-infectious causes

Less frequently, fever can be driven by autoimmune diseases, medication-induced fever, heat exhaustion, or rarely, blood clots or certain cancers.

Symptom combinations: what they can mean

• Fever + cough + shortness of breath/chest pain: Possible pneumonia – seek prompt medical care
• Fever + severe headache + stiff neck + sensitivity to light: Possible meningitis – call emergency services immediately
• Fever + rash (especially purple or non-blanching spots): May indicate severe infections – seek emergency care
• Fever + chills + feeling very unwell: Could signal sepsis – urgent evaluation recommended
• Fever + burning when urinating + flank/back pain: Suggests kidney infection – see a doctor soon
• Fever + vomiting/diarrhea + dizziness/dry mouth: Signs of dehydration – drink plenty of fluids

Safe self-care at home

Not every episode of fever is dangerous. Many mild infections can initially be managed at home.

Fluids and rest

• Drink enough fluids: water, tea or diluted fruit juices
• If nauseated, sip small amounts frequently rather than large volumes at once
• Rest and avoid strenuous physical activity
• Wear light clothing and keep the room comfortably cool

Cooling measures

Cool compresses, lukewarm showers or sponging can make you feel more comfortable. Avoid ice-cold baths or alcohol rubs.

Medication safety: paracetamol and ibuprofen

• Paracetamol: Adults commonly take 325–1000 mg per dose. Do not exceed 3–4 g per day.
• Ibuprofen: Many adults use 200–400 mg per dose. Without medical supervision, do not exceed 1,200 mg per day.
• Avoid double-dosing: Many cold and flu remedies already contain these ingredients.

If you recently travelled to an area with dengue fever, avoid ibuprofen and aspirin because of increased bleeding risk.

When to seek medical help

Contact a healthcare provider if:

• Your fever is above about 39–39.5 °C for more than 1–2 days
• Your fever (above 38 °C) lasts longer than 3 days without a clear cause
• Your fever does not improve with acetaminophen or ibuprofen
• You develop new symptoms such as severe sore throat, ear pain, productive cough

Seek emergency care if fever is accompanied by:

• Shortness of breath, wheezing, very rapid breathing or blue lips
• Confusion, difficulty staying awake, seizures
• Severe headache with stiff neck or light sensitivity
• Severe chest pain or sudden, intense abdominal pain
• Purple or non-blanching spots on the skin
• Signs of severe dehydration

Special risk groups

People who should seek medical advice earlier include:

• Pregnant women
• People with weakened immune systems
• People with serious chronic illnesses
• Older adults, especially those over 75 years

FAQ: Common questions about fever in adults

Is fever always bad?

No. Mild fever is often a sign that the immune system is working. What matters more are the underlying cause, how you feel overall and how long the fever lasts.

Why is my fever higher at night?

Body temperature naturally follows a daily rhythm and tends to be higher in the evening. Infections can amplify this pattern.

How long does fever from flu or COVID-19 usually last?

In uncomplicated cases, fever and intense malaise often improve within about 3–7 days. If fever persists longer or you feel worse, seek medical care.