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Fever in Adults: When to Worry, Symptoms, and Causes

6 min read

By Patty Weasler, RN

We’ve all had a fever at least once. It’s so uncomfortable, we sweat, feel hot but then get the chills and can’t seem to warm up. When we have a fever it might seem like our body is fighting against us. But it turns out our body is doing us a favor by inducing the fever. A fever is a symptom of numerous illnesses that are characterized by an elevated body temperature. The increased body temperature is one of the ways our body’s immune system activates to fight the illness.

Perhaps by having a better understanding of fevers we can learn how to appreciate our body’s immune system. In this article, we’ll cover fever in adults: when to worry as well as all the symptoms and causes you should know.

What Is a Fever?

Let’s start at the beginning and break down what a fever is. A fever is when your body temperature is higher than normal. The Cleveland Clinic tells us that in adults, a fever is classified as a temperature higher than 100.4-degrees Fahrenheit (38-degrees Celsius). For reference, a normal body temperature is 98.6-degrees Fahrenheit (37-degrees Celsius).

When we have a high temperature it is our body’s natural way of fighting an infection. According to Healthline “A fever begins when your immune system makes more white blood cells to fight an infection. The increase in white blood cells triggers your brain to heat your body up.” With the increase in body temperature, you will experience symptoms of a fever such as shivering, sweating, and body aches.

Symptom: Elevated Temperature

The most common symptom of a fever is an elevated temperature. As we mentioned above, a temperature of 100.4-degrees Fahrenheit (38-degrees Celsius) is considered a fever. The increased temperature can make you feel hot. As your temperature rises your body’s metabolism also increases, this means you will need more oxygen and nutrients for your tissues and muscles to stay healthy. To achieve this your heart rate will increase in order to bring those vital nutrients and oxygen.

It turns out our brain is what controls our body temperature. According to Harvard Health, “A part of the brain called the hypothalamus acts as the body’s thermostat. When all is well in the body, the hypothalamus is set at the normal body temperature. Fever develops when the hypothalamus is set to a higher-than-normal temperature.” Our body is a complex system that works to keep us healthy and safe. Though an increased temperature may feel uncomfortable, it is one of the many ways our body works to fight infections.

Symptom: Chills, Shaking, and Shivering

As an adult, a fever can really take you on by surprise. Many adults forget how miserable fevers can make them feel. The chills, shaking, and shivering makes it hard to sleep and get that much-needed rest. But it turns out the shivering and shaking are all a part of your body’s plan to fight off that infection.

Shivering actually causes your temperature to rise. The quick contraction and relaxation of your muscles create heat. “It’s an involuntary response triggered by your immune system reacting to an infection or a cold environment,” says Healthline.

Chills on the other hand are the result of a fever and not a cause. Chills can feel strange — you may feel warm on the inside but your skin is cold. This is actually for a good reason! When you have a fever the blood vessels near your skin contract or become smaller. Your body is focusing on bringing blood to areas of the body it deems important like your brain, lungs, and heart. It diverts blood away from areas it deems unimportant like your skin. This causes your skin to feel cold and gives you chills.

Symptom: Fatigue

You not only have a fever and chills but now you are so tired you can hardly get out of bed. Fatigue with a fever is a very real symptom and one that you probably shouldn’t ignore. Your body is in overdrive when its temperature is elevated causing you to feel fatigued.

Take time to rest when you are tired with a fever. Sleep and rest will help you restore and heal. If you are a busy person with appointments, work, and social events, then it’s time to call those off until your fever subsides. Running around will not only make you feel worse but if your fever is from a contagious infection you are likely to pass that on to others as well.

Symptom: Headache and Body Aches

It’s the morning and you wake up feeling warm, tired, and your body just aches. You have a fever and now the symptoms are in full swing. According to Health Grades, “body aches are dull pain or discomfort in part or all of the body.” They can range from mild to feeling like you were hit by a bus. For many people, the aching doesn’t stop in their body, it continues to the head.

A headache is another common symptom of a fever. If you suffer from body aches or headaches it’s time to slow down and give yourself some time to heal.

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Symptom: Sweating

Have you heard of the phrase, “sweat it out”? It’s usually referencing sweating out a fever. However, the thought behind this phrase and practice doesn’t hold up. A fever can make you sweat but sweating will not cure your fever. It would actually cause you to become dehydrated and feel worse if you intentionally make yourself sweat more.

Your body sweats when it has a fever in an effort to cool you down. According to Scientific American, “The necessary heat of evaporation is extracted from the sweat itself, which leads to a heat transfer from the liquid into the gaseous state. This results in a cooling effect (called evaporative cooling) that helps to maintain body temperature and cools the body down when it gets too hot.” In layman’s terms: as sweat evaporates from your skin it cools you down.

Causes: Infection

Now that we have covered the symptoms of a fever it’s time to talk about what causes a fever. A fever is primarily caused by an infectious source. This could be a bacterial, viral, or inflammatory disease like rheumatoid arthritis or Crohn’s disease. Many times a fever is a good thing, it can be one of the first signs of an illness and we know that our immune system is working to fight the infection.

Did you know that most infections can only survive in our body when it is at a normal temperature? Medline Plus tells us that “You get a fever because your body is trying to kill the virus or bacteria that caused the infection.” Our body is an amazing system. It works hard to keep us healthy and safe in so many different ways.

Non-Infectious Causes

Infections aren’t the only cause of fever in adults. Several non-infectious sources can make your body temperature go up too.

Some non-infectious causes of a fever include stress, some immunizations, a serious sunburn, blood clots, and food poisoning. In many cases, it can be difficult to pinpoint the cause of your fever and in those scenarios, it’s time to call your healthcare professional.

When You Can Treat a Fever at Home

If you have a mild fever that is self-limiting, meaning it is not causing any other issues then you may be able to treat it at home with a few simple home remedies. A fever-reducing medication like acetaminophen (Tylenol) and a non-steroidal anti-inflammatory medication like ibuprofen (Advil) can be helpful to ease your fever. Pair a medication along with plenty of fluids, rest, and a cool compress for your forehead, and let yourself have time to recuperate.

When you have a fever, the best thing you can do is rest. Unfortunately, that is one of the hardest things for people to do. Call in sick to work, ask friends and family for help, and do whatever it takes to let your body heal.

How to Know When a Fever is Serious

So how do you know when your fever is a sign of something more serious? According to Healthline, you should call your doctor if your temperature is greater than 103-degrees Fahrenheit (39.4-degrees Celsius), you’ve had your fever for more than three days, if you have a serious underlying medical condition, or if you’ve recently been to a different country.

Fevers can also cause serious problems that require an emergency room visit. Some of these side effects include seizures, severe headaches, loss of consciousness, hallucinations, swelling, or confusion. If you are unsure if your fever is serious, call your doctor to help determine the best course of action.

Prostock-studio / Shutterstock


Patty is a freelance health writer and nurse (BSN, CCRN). She has worked as a critical care nurse for over 10 years and loves educating people about their health. When she's not working, Patty enjoys any outdoor activity that she can do with her husband and three kids.

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