10 Common Fever Symptoms You Should Know and When to Seek Help

A fever is one of the most common signs that your body is fighting an infection or illness. While most people recognize the feeling of being hot and uncomfortable, fever comes with a variety of symptoms that can help you understand what’s happening in your body. Understanding these symptoms can help you determine when to rest at home and when to seek medical attention.

Fever occurs when your body’s temperature rises above its normal range, typically considered to be 98.6°F (37°C). Most healthcare providers consider a temperature of 100.4°F (38°C) or higher to be a fever. However, the symptoms accompanying a fever can be just as important as the temperature reading itself. Let’s explore the most common symptoms you might experience when you have a fever.

1. Elevated Body Temperature

The hallmark symptom of fever is an elevated body temperature above the normal range. A temperature of 100.4°F (38°C) or higher measured orally is generally considered a fever. However, what constitutes a fever can vary slightly depending on where you measure it:

• Oral temperature: 100.4°F (38°C) or higher
• Rectal temperature: 100.4°F (38°C) or higher (most accurate)
• Armpit temperature: 99°F (37.2°C) or higher
• Ear temperature: 100.4°F (38°C) or higher

A fever of 103°F (39.4°C) or higher in adults is considered high and warrants closer attention. The temperature may fluctuate throughout the day, often being lower in the morning and higher in the late afternoon and evening. Your body temperature is regulated by the hypothalamus in your brain, and when it detects infection or illness, it raises your body’s thermostat to help fight off invaders.

2. Chills and Shivering

Chills are one of the most recognizable symptoms accompanying fever. You may feel intensely cold and start shivering uncontrollably, even when the room temperature is comfortable or when your body temperature is actually elevated. This seemingly contradictory symptom occurs because your brain has reset your body’s internal thermostat to a higher temperature.

When your body is trying to reach this new, higher set point, your muscles contract rapidly to generate heat through shivering. You might pile on blankets and still feel cold. These chills can range from mild to severe and may come in waves. Once your body temperature reaches the new set point, the chills typically subside. When your fever breaks and your body temperature starts to return to normal, you may experience the opposite sensation and begin sweating profusely.

3. Sweating

Excessive sweating often occurs during a fever, particularly when the fever is breaking or subsiding. This is your body’s natural cooling mechanism attempting to lower your elevated temperature back to normal levels. You may wake up drenched in sweat, require multiple changes of clothing, or need to change your bed sheets.

Sweating during a fever serves an important purpose in thermoregulation. As the moisture evaporates from your skin, it helps dissipate heat and cool your body down. While this is uncomfortable, it’s actually a positive sign that your body is working to regulate its temperature. However, excessive sweating can lead to dehydration if you’re not replacing the lost fluids, making it important to drink plenty of water and other hydrating beverages when you have a fever.

4. Headache

Headaches are an extremely common symptom that accompanies fever. The pain can range from a dull, persistent ache to a more intense, throbbing sensation. Fever-related headaches typically affect the entire head rather than being localized to one specific area.

Several factors contribute to fever-induced headaches. The elevated body temperature can cause blood vessels in the brain to dilate, leading to increased pressure and pain. Dehydration, which often accompanies fever due to increased sweating and reduced fluid intake, can also trigger or worsen headaches. Additionally, the inflammatory chemicals released by your immune system when fighting infection can contribute to head pain. The headache may intensify with physical activity or sudden movements and often improves as the fever subsides.

5. Muscle Aches and Body Pain

Generalized muscle aches, also known as myalgia, are frequently reported by people experiencing fever. You may feel soreness, stiffness, or pain throughout your body, particularly in your back, arms, and legs. This discomfort can make even simple movements feel challenging and exhausting.

These muscle aches occur because your immune system releases chemicals called cytokines and interleukins when fighting infection. While these substances are crucial for combating illness, they can also cause inflammation in muscle tissues, leading to pain and discomfort. Your muscles may feel weak and tired, similar to how you might feel after an intense workout. The severity of muscle aches can vary depending on the underlying cause of your fever and may be accompanied by joint pain as well. Rest is particularly important when experiencing this symptom, as your body needs energy to fight off whatever is causing your fever.

6. Fatigue and Weakness

Overwhelming tiredness and a general feeling of weakness are hallmark symptoms of fever. You may feel completely drained of energy, struggle to complete normal daily activities, and need to spend most of your time resting or sleeping. This isn’t ordinary tiredness – it’s a profound exhaustion that affects both your physical and mental capacity.

This fatigue occurs for several reasons. First, your body is diverting significant energy resources toward fighting the infection or illness causing your fever. Your immune system is working overtime, which requires substantial energy expenditure. Second, the elevated body temperature itself increases your metabolic rate, meaning your body burns through energy faster than normal. Third, the disrupted sleep that often accompanies fever prevents your body from getting the restorative rest it needs. This combination of factors can leave you feeling completely depleted. Listening to your body and allowing adequate rest is crucial for recovery.

7. Loss of Appetite

A decreased desire to eat is a very common symptom when you have a fever. Foods that normally appeal to you may seem unappealing or even unappetizing. You might feel nauseous at the thought of eating or simply have no interest in food at all. Some people can only tolerate bland, simple foods when feverish.

This loss of appetite is actually part of your body’s natural defense mechanism. Research suggests that reducing food intake during illness may help your immune system function more effectively. When you’re not digesting food, your body can redirect energy toward fighting infection. Additionally, the inflammatory chemicals released during illness can affect the parts of your brain that regulate hunger, actively suppressing your appetite. While it’s important to stay hydrated, don’t force yourself to eat large meals if you’re not hungry. Small amounts of easily digestible foods like broth, toast, or crackers can help maintain your energy without overwhelming your system.

8. Dehydration

Dehydration frequently occurs alongside fever and can actually worsen your other symptoms. Signs of dehydration include dry mouth, decreased urination, dark yellow urine, dry skin, dizziness, and increased thirst. In severe cases, you might experience confusion or rapid heartbeat.

Several factors contribute to dehydration during a fever. Your elevated body temperature increases fluid loss through your skin. Sweating, which often accompanies fever, depletes your body’s water stores. Additionally, the reduced appetite and nausea that often occur with fever can make it difficult to maintain adequate fluid intake. Breathing faster due to fever also increases moisture loss through respiration. Dehydration can create a vicious cycle, as it can make your fever harder to control and worsen symptoms like headaches and fatigue. Drinking plenty of water, clear broths, or electrolyte-containing beverages is crucial when you have a fever, even if you don’t feel thirsty.

9. Rapid Heart Rate

An increased heart rate, also called tachycardia, commonly occurs with fever. You might notice your heart beating faster than usual, even when you’re resting. For every degree Fahrenheit your temperature rises above normal, your heart rate typically increases by about 10 beats per minute.

This increased heart rate serves several purposes in your body’s response to fever. Your heart pumps faster to circulate blood more rapidly throughout your body, helping to distribute immune cells to fight infection and regulate body temperature. The elevated metabolic rate that accompanies fever also requires your cardiovascular system to work harder to meet your body’s increased oxygen and nutrient demands. While a moderately increased heart rate is normal with fever, a very rapid or irregular heartbeat, especially if accompanied by chest pain or severe shortness of breath, requires immediate medical attention.

10. Irritability and Difficulty Concentrating

Changes in mood and mental function are often overlooked symptoms of fever. You may feel unusually irritable, short-tempered, or emotionally sensitive. Tasks that normally require little mental effort may seem overwhelming or impossible to complete. You might have difficulty focusing, experience brain fog, or feel confused and disoriented.

These cognitive and emotional changes occur because fever affects brain function in several ways. The elevated temperature can interfere with normal neurotransmitter activity, affecting mood regulation and cognitive processing. The inflammatory chemicals circulating in your bloodstream can cross into the brain and impact mental clarity. Additionally, the fatigue, discomfort, and disrupted sleep that accompany fever all contribute to irritability and reduced mental sharpness. In children, fever can sometimes cause more dramatic behavioral changes, including unusual fussiness or lethargy. While mild irritability and brain fog are normal, severe confusion, hallucinations, or extreme agitation warrant immediate medical evaluation.

Common Causes of Fever

Understanding what causes a fever can help you better manage your symptoms and determine when medical attention is necessary. Fever itself is not an illness but rather a symptom indicating that your body is responding to something. Here are the most common causes:

Viral Infections

Viral infections are the most frequent cause of fever in both children and adults. Common viral illnesses that cause fever include:

• Common cold and influenza (flu)
• COVID-19
• Gastroenteritis (stomach flu)
• Respiratory syncytial virus (RSV)
• Mononucleosis
• Viral meningitis

Bacterial Infections

Bacterial infections often cause higher fevers than viral infections and may require specific medical treatment. Common bacterial causes include:

• Strep throat
• Urinary tract infections (UTIs)
• Pneumonia
• Ear infections
• Sinus infections
• Skin infections
• Bacterial meningitis

Immunizations

Fever is a common side effect of many vaccines. This is actually a sign that your immune system is responding appropriately to the vaccine and building protection. Vaccine-related fevers typically appear within 24 hours of vaccination and resolve within a day or two.

Other Causes

Less common but important causes of fever include:

• Heat exhaustion or heat stroke
• Inflammatory conditions (such as rheumatoid arthritis or inflammatory bowel disease)
• Certain medications (drug-induced fever)
• Blood clots
• Cancer, particularly leukemia and lymphoma
• Autoimmune disorders
• Teething in infants (though this typically causes only low-grade fever)

Prevention Strategies

While you cannot prevent all fevers, you can reduce your risk of developing infections that cause fever by following these preventive measures:

Practice Good Hygiene

Proper hand hygiene is one of the most effective ways to prevent infections. Wash your hands frequently with soap and water for at least 20 seconds, especially before eating, after using the bathroom, and after being in public places. If soap and water aren’t available, use an alcohol-based hand sanitizer containing at least 60% alcohol.

Avoid Close Contact with Sick People

When possible, maintain distance from people who are ill. If someone in your household is sick, try to limit sharing of personal items like towels, drinking glasses, and eating utensils. Clean and disinfect frequently touched surfaces regularly.

Stay Up to Date with Vaccinations

Vaccines are one of the most effective tools for preventing many infections that cause fever. Ensure you and your family members are current on recommended immunizations, including:

• Annual influenza vaccine
• COVID-19 vaccine and boosters
• Routine childhood vaccinations
• Pneumococcal vaccine for eligible adults
• Other vaccines recommended by your healthcare provider

Maintain a Healthy Lifestyle

A strong immune system is better equipped to fight off infections. Support your immune health by:

• Getting adequate sleep (7-9 hours for adults)
• Eating a balanced diet rich in fruits, vegetables, and whole grains
• Exercising regularly
• Managing stress through relaxation techniques
• Avoiding smoking and limiting alcohol consumption
• Staying well-hydrated

Practice Food Safety

Foodborne illnesses can cause fever. Reduce your risk by properly storing, handling, and cooking food. Wash fruits and vegetables thoroughly, cook meat to appropriate temperatures, and refrigerate perishables promptly.

Protect Yourself from Insect Bites

Some fevers result from insect-borne illnesses. When in areas with mosquitoes or ticks, use insect repellent, wear protective clothing, and check for ticks after spending time outdoors.

Frequently Asked Questions

What temperature is considered a fever?

A fever is generally defined as a body temperature of 100.4°F (38°C) or higher when measured orally. However, normal body temperature can vary slightly from person to person and throughout the day. Rectal temperatures tend to be about 0.5-1°F higher than oral temperatures, while armpit temperatures are typically about 0.5-1°F lower.

How can I tell if I have a fever without a thermometer?

While using a thermometer is the most accurate way to detect fever, you may suspect a fever if you experience hot, flushed skin (especially on the forehead, neck, or chest), sweating, chills, body aches, fatigue, or general feelings of being unwell. However, these symptoms alone cannot confirm a fever or determine its severity, so using a thermometer is recommended when possible.

Is a fever of 103°F dangerous?

A fever of 103°F (39.4°C) in adults is considered high and should be monitored closely. While uncomfortable, it’s not automatically dangerous for most adults unless it persists for several days or is accompanied by severe symptoms like difficulty breathing, chest pain, severe headache, confusion, or persistent vomiting. For children, especially infants under 3 months, any fever requires prompt medical evaluation. Always consult with a healthcare provider if you’re concerned about a high fever.

When should I see a doctor for a fever?

Seek medical attention if you experience a fever accompanied by severe headache, stiff neck, difficulty breathing, chest pain, persistent vomiting, confusion, seizures, or a rash. Adults should see a doctor if fever exceeds 103°F (39.4°C), lasts more than three days, or returns after subsiding. For infants under 3 months, any fever of 100.4°F (38°C) or higher requires immediate medical evaluation. People with compromised immune systems should contact their healthcare provider promptly when fever develops.

Why do fevers often get worse at night?

Fevers typically peak in the late afternoon and evening due to your body’s natural circadian rhythm. Your body temperature naturally fluctuates throughout the day, being lowest in the early morning and highest in the late afternoon. When you have a fever, this pattern becomes more pronounced. Additionally, lying down and being less active at night may make you more aware of fever symptoms. The body’s inflammatory response also tends to be more active during evening hours.

Can you have a fever without an infection?

Yes, while infections are the most common cause of fever, other conditions can also raise body temperature. These include autoimmune disorders, certain cancers, heat exhaustion, reactions to medications, blood clots, and inflammatory conditions. Some people develop fever after intense physical activity or prolonged sun exposure. Teething in babies may cause mild temperature elevation, though this remains somewhat controversial among healthcare providers.

Should I try to lower my fever?

Mild to moderate fevers (under 102°F or 38.9°C) generally don’t need to be treated unless causing significant discomfort. Fever is actually a helpful immune response that helps your body fight infection. However, if the fever is causing considerable discomfort, interfering with sleep or hydration, or is very high, you may want to take measures to reduce it. Focus on staying hydrated, resting, and staying comfortable. If you’re considering medication to reduce fever, consult with your healthcare provider, especially for children.

How long does a fever typically last?

The duration of a fever depends on its underlying cause. Viral infections, the most common cause, typically produce fevers lasting 3-4 days, though they can occasionally persist for up to a week. Bacterial infections may cause fever until appropriate treatment is started. A fever lasting more than three days in adults or more than 24 hours in children under 2 years old should be evaluated by a healthcare provider. If fever returns after subsiding, this also warrants medical attention.

Is it safe to exercise with a fever?

No, exercising with a fever is not recommended. When you have a fever, your body is already working hard to fight infection, and your heart rate is elevated. Adding the stress of exercise can strain your cardiovascular system, worsen dehydration, and potentially delay recovery. Exercise can also temporarily raise body temperature further, making you feel worse. Wait until your fever has been gone for at least 24 hours and you’re feeling significantly better before resuming physical activity, and then start slowly.

References:

• Mayo Clinic – Fever: Symptoms and Causes
• Johns Hopkins Medicine – Fever
• Centers for Disease Control and Prevention – Fever Information
• NHS – Fever in Adults
• Cleveland Clinic – Fever
• MedlinePlus – Fever