The Flu: Symptoms, Causes, and Treatment

By the time we’re adults, most of us have gotten sick with at least a few colds and a more severe viral infection called the flu. The flu is one of the most long-lasting and common viruses in the world, being active on every continent except Antarctica and causing a variety of uncomfortable symptoms, like fever, body aches, and sore throat. The flu originally spread worldwide during the influenza pandemic of 1918 and 1919.

But although we all have an encounter with the flu sooner or later, most of us don’t know much about this virus or what we can do to minimize our odds of catching it again. Let’s take a much closer look at the flu, examining its symptoms and causes. We’ll also go over flu vaccines and the kinds of medicine you should prioritize when treating the flu in yourself or your children.

What is the Flu?

The flu, short for influenza, is a type of viral respiratory infection and is among the most common to infect humans. As a respiratory infection, it typically targets your throat, lungs, and nose, settling in those regions to replicate.

When you are infected with the flu, the influenza virus quickly targets healthy cells in your lungs and throat, injecting those cells with its own genetic material called RNA (similar to DNA). The infected cells are then hijacked and will then replicate and spread the flu virus even further. Your immune system normally recognizes this infectious disease quickly and begins physiological countermeasures, such as starting a fever and flooding the infected areas with white blood cells.

Many of the symptoms associated with the flu, such as a fever and a sore throat, are actually caused as a result of your immune system’s defenses. For example, the immune system begins a fever to make your body less hospitable for the flu virus. Under extreme heat, flu viruses break down and are easier to destroy for your immune system.

The flu is classified as a very narrow range of viruses. Many people also call stomach bugs “the flu”, although this is not accurate. Technically, “stomach flu” viruses are totally different and may cause different symptoms.

There are a variety of different flu viruses because the core flu species mutates relatively frequently, meaning it’s wise to get vaccinated for the annual strain of flu every year. The flu’s symptoms are usually uncomfortable but typically resolve on their own. Most healthy adults and children are not particularly at risk for intense side effects or flu complications.

But there are certain subsets of the population who are at a higher risk of flu complications, associated risks, and hospitalizations. These high-risk individuals include:

• Older adults over the age of 65
• Children under the age of five
• Pregnant women
• Those with weakened immune systems or those with autoimmune health conditions
• People with chronic medical conditions like heart disease or kidney disease
• Obese individuals with a BMI (body mass index) of over 40
• People with chronic lung disease or asthma

Flu Symptoms

Flu symptoms are very recognizable and tend to begin very quickly. On average, flu symptoms appear around 2 days after contracting the virus, although it can take anywhere from 1 to 4 days to experience flu symptoms.

The most common symptoms of the flu include:

• Fever, especially a high fever above 100°F
• Severe aching in the joints and muscles, particularly the limbs
• Stuffy nose or clogged sinuses
• Tiredness or fatigue
• Chills
• Headaches or migraines
• Coughing, either wet or dry (though usually dry)
• Sore throat
• Runny nose
• Warm, flushed, and red skin

Additionally, most adults with a typical seasonal flu strain will not have stomach-related symptoms. Children can sometimes experience stomach aches, nausea, or diarrhea, and other symptoms with a regular flu strain as opposed to the "stomach flu". People will often have stomach problems with COVID-19 as well which can help to differentiate it from the flu.

Although the above symptoms can be quite uncomfortable, it is not normally necessary to contact a doctor, whether you or your child has the disease. However, more serious symptoms include:

• Pain or pressure in the stomach area or the chest
• Intense or sudden dizziness
• Difficulty breathing or talking
• Intense confusion or lack of awareness
• Muscle pain
• Severe vomiting

If you or your child experiences any of these symptoms, it is a good idea to contact a doctor. It may indicate that there is something else working alongside the flu or that your body is not handling the illness as efficiently as it should.

How Can I Tell If My Child Has The Flu?

Kids contract a variety of diseases from their outdoor play and their contact with other kids at school or in other social environments. Furthermore, children's immune systems are not as developed as adults', so they're more likely to get yearly or seasonal strains of common diseases like a cold or the flu.

However, it can be difficult to tell whether your child has the flu or a cold, especially if they don’t know how to describe their symptoms. You can tell that your child has the flu if:

• Their fever lasts for three or four days in total as opposed to one or two nights. Flu fevers are typically more intense than cold fevers
• More intense aches
• General fatigue or exhaustion
• Dry coughs without sneezing. Colds typically cause the body to produce more mucus compared to the flu
• Intense headaches, which are more common with the flu and rarer with a cold

Furthermore, you can consider the time of year during which your child becomes sick. If your child is sick during flu season (more on that below), they may be suffering from the flu instead of a typical cold.

Does the Flu Always Come With a Fever?

No, although it usually does.

At its core, a fever is a biological response induced by your brain’s hypothalamus (which essentially acts as the body’s temperature regulator). Your immune system kick starts a fever when it detects the presence of a virus spreading throughout your body.

By increasing your body’s internal temperature, a fever can make viruses break down and “denature.” This both assists your immune system with removing the infection overall and makes it more difficult for the virus to spread unchecked.

However, a fever is also a mildly dangerous countermeasure. If left to increase without stopping, a fever can cause bodily damage and even be lethal. You might not experience a fever if the current flu infection is relatively mild or if the body can fight off the virus without raising the temperature.

Most doctors consider any temperature over 100.4°F to be a sign of a fever, as the typical bodily temperature range can be anywhere between 97 - 100°F. But fevers in children often run at higher temperatures compared to fevers and adults, usually between 103°F and 105°F.

If you or your child has the flu but do not also experience a fever, it may just be a sign that the current flu infection will be dealt with more swiftly than average.

Flu Causes

All cases of the flu are caused by the influenza virus: a species of a viral cell that comes in a wide range of subtypes and subspecies. There are two main types of influenza: influenza A and influenza B. Of these, Type A influenza is the most serious and has the greatest potential for life-threatening complications and widespread outbreaks.

Influenza A is the type we are most familiar with. It includes all the common symptoms and signs of a flu infection, such as a fever, aches, headaches, and fatigue. Influenza B can also induce severe symptoms, but it is less common than influenza A during the normal, annual flu season.

This is partially because influenza B viruses mutate at a much slower rate compared to influenza A viruses. As a result, they can be more easily identified by the immune system and are less likely to reach an infectious point before being removed. Influenza A mutates much more quickly, so each year our immune systems have to learn what the “new flu” looks like before acquiring immunity.

Influenza A viruses can be carried by birds (though not always) and the virus can sometimes spread from these animals to humans. Influenza B viruses are naturally carried by humans, which also help to explain our general immunity to these viruses.

Influenza C viruses are a third type of influenza virus. Influenza c is the rarest and also causes minor symptoms.

Regardless, any influenza virus causes symptoms by infecting healthy cells in your respiratory system, such as your lungs, throat, and nose. When this occurs, monitoring cells from your immune system signal that an infection is taking hold. Your immune system implements several defenses, such as a fever or swelling of the throat, in order to flush out the virus and remove all of its cells from the body.

In the midst of the infection, your body will need much more energy than it normally does, so you may feel more fatigued, even if you spend all day lying down.

What To Eat If You Have The Flu

Many people lose their appetites when they become sick with the flu (or any disease). However, it’s important to maintain a healthy diet while you are sick with the flu, as food provides your body with new energy so it can continue to function and so your immune system can fight off the infection.

Certain foods are more palatable or helpful for your body when you are infected with the flu. These include:

• Broth, whether it’s beef, chicken, or vegetable broth. Broth is easy for your stomach to digest, feels soothing to the throat when served warm, and provides your body with a number of nutrients for energy. In addition, broth can prevent dehydration: a key concern when in the midst of a fever, which causes your body to become dehydrated more quickly
• Chicken soup, which provides many of the same benefits as broth with more fibrous foods, like certain vegetables. It also contains additional nutrients from vegetables and from chicken. Chicken soup with low salt content is preferred
• Garlic, which some studies show can enhance your immune system and reduce the severity of several flu symptoms
• Yogurt that includes live cultures of probiotics or helpful bacteria. This can boost your immune system and help your gut recover from a flu infection
• Fruits that include vitamin C, which is one of the most important nutrients for your immune system’s overall health. These fruits include citrus fruits, tomatoes, and strawberries
• Broccoli is one of the best green vegetables to eat when sick with the flu. It includes not only vitamin C but also vitamin E, a key antioxidant, as well as plenty of fiber and calcium
• Spicy food if you have intense congestion and your throat is not particularly sore. Spicy foods like pepper and horseradish can break up congestion and make it easier to breathe

While all of the above foods can be a great choice to maintain optimal nutrition, you should also make sure to drink plenty of water, even if you eat lots of broth or chicken soup. Your body needs extra water when sick so it can pass waste products more frequently and so you don’t become dehydrated because of your fever, coughing, or sneezing.

Drinking more water will also soothe your throat more frequently.

What is “Flu Season” and When Does It Start?

“Flu season” is simply the time of year when influenza viruses are most active and when humans are most likely to get infected by the yearly strain of influenza Type A.

Flu season in the United States and other Northern Hemisphere countries is during the winter, typically marked by the months between October and March. The Centers for Disease Control and Prevention (CDC) notes that influenza activity peaks between December and February, although higher than average spikes can persist until as late as May.

In general, any colder months or weather throughout the year makes it easier for influenza viruses to spread either from animals to humans or from person-to-person. Note, however, that influenza can still be caught at any point during the year. Influenza circulates through the human population all year round and may cause a few infections or hotspots here and there until official flu season.

Scientists don’t yet know why the flu spreads more due to cold weather brought about by the winter. It may be because the flu virus can survive on exposed surfaces outside the body for longer in lower temperatures (including hard surfaces or on organic matter, such as bird feathers). It may also be because the strength of immune systems dip slightly with the lower light level during the winter months, making us marginally more vulnerable to infections of any type.

For flu vaccine purposes, the CDC declares flu season to begin once there is a significant spike in influenza infections throughout the country. During flu season, the CDC tracks and monitors the flu infection rate in the country and begins studying people who are infected with the virus.

Using all the data it gathers, the CDC attempts to forecast viral peaks and develop a new virus for the yearly strain.

How Long is the Flu Contagious?

One of the most effective aspects of the flu is its high contagiousness. It’s very easy for this virus to spread from person-to-person both because of how easily it attaches to human cells and because of how long people are contagious after being infected with influenza.

In fact, individuals are contagious with the flu from the moment they are infected, not from when they know they are sick. Flu symptoms typically last for between 3 and 7 days although minor symptoms like cough can last for 2 weeks or longer. Symptoms first appear between 1 and 4 days after initial exposure to the virus, and then symptoms can last an additional 5 to 7 days depending on the infection’s severity.

It is possible to infect another person with the flu at least one day before your symptoms develop. However, the flu is most contagious in the first 3 to 4 days after symptoms first appear, or during the peak symptom period. During this period, individuals are most likely to sneeze or cough more often, which can spread the virus.

It’s also important to note that it’s possible to infect someone with the flu as your symptoms gradually alleviate and disappear. The flu may even be contagious some days after symptoms totally vanish. Therefore, it’s important to give yourself several days of apparently healthy recovery time before returning to social hubs, as you may still be contagious even if you don’t experience any flu symptoms.

Furthermore, children or adults who have weakened immune systems are more likely to infect other people with flu viruses for an extended period of time. Stray viruses can be missed by their immune systems and remain in bodily fluids like saliva for much longer.

Should I Still Send My Child To School If They Have the Flu?

No. Not only is it a bad idea for social reasons (your child is likely to infect other children and teachers if they have the flu), but it may also be forbidden by your child's school. Flu infections can progress rapidly and it’s not uncommon for a single infected individual to spread the virus to dozens or even hundreds of people due to irresponsibility.

As we have seen during the coronavirus pandemic, viral infections can be spread through even short periods of close contact.

If your child has the flu, you should instead allow them to stay home for at least five days, and possibly up to a week or more depending on how their infection progresses. Chances are that your child may have infected others by the time they start to develop symptoms if they have been at school regularly.

But you should minimize the possibility of additional infections by keeping them home and effectively quarantining them. Furthermore, it’s smarter to let your child rest and recuperate at home, where you can monitor their hydration and nutrition, than it is to make them expend energy at school.

Not only is your child less likely to perform academically well at school when they are sick with the flu, but their infection may last for longer if you force them to attend school since their bodies will be fatigued and weakened from expending lots of unnecessary energy.

Bottom line: bring your child home and allow them to recover under your supervision rather than keeping them at school if they contract the flu.

Why Does the Flu Go Away In The Summer?

Just as scientists are not fully aware of why the flu seems to spike in the winter, they do not fully understand why it seems to have the opposite effect in the summer. The summer months bring a noticeable dip in influenza cases and you are less likely to catch the flu during the months from April to September in the northern hemisphere.

This is probably related to the ideal temperature for the influenza virus. Summer heat likely makes it difficult for the virus to survive on exposed surfaces for too long, so transferring the virus from person-to-person or from bird to human is more difficult.

However, remember that it is not impossible to catch the flu in the summer, and summertime flu is in no way less severe than winter flu. Additionally, note that seasonal influenza trends are reversed for the southern hemisphere. The traditionally warm months in the northern hemisphere are cold in southern hemisphere countries like Brazil and Australia, so those countries have a flu season opposite to the one experienced by the United States.

Flu Shot Basics

The “flu shot” or flu vaccine is a key public health initiative that has been around for decades at this point. The influenza vaccine is important because immunization in the majority of the public achieves “herd immunity." While anyone can suffer from serious complications, herd immunity is especially important to protect those with higher risk factors from coming into contact with the flu and developing severe illness.

In a nutshell, herd immunity means that the majority of people in a population (such as a city, state, or country) are immune to a particular virus. When herd immunity is achieved, it’s very difficult for the virus to transfer to any at-risk individuals, such as children, the elderly, or those with compromised immune systems. Herd immunity can only be achieved through collective social responsibility – almost everyone who can get vaccinated must be vaccinated for herd immunity to be effective.

The flu shot is an annual vaccine developed by the CDC and other medical organizations. It takes into account mutation changes for yearly flu and gives your immune system a way to counteract the illness before it comes into contact with a “live” version.

The seasonal flu vaccine is developed to protect against new annual flu viruses and certain viral strains that may be reintroduced in the population from time to time. These include:

• H1N1 or swine flu
• H3N2
• 2 influenza B viruses

Flu Vaccines: A Primer

As with all other vaccines, the flu vaccine works by causing your immune system to develop antibodies to the yearly flu strain. Antibodies are your immune system’s natural defense against viruses.

Under normal circumstances, the process works like this:

• Your immune system detects the presence of a virus
• Your body starts to experience symptoms of the disease while your immune system develops antibodies to fight the viral cells off
• The newly developed antibodies defeat the infection and you recover

When you are given a vaccine, doctors give your body “dead” or inactive viral cells for a particular disease. The cells are totally harmless, but they are still recognizable by your immune system, which automatically develops antibodies against the live version of the disease.

Then, if your body ever encounters the live version of the disease, your immune system already has antibodies in place and can fight off the infection before it takes root. In this way, vaccines have allowed humans to overcome countless dangerous and deadly diseases, including polio and deadly strains of the flu virus, such as the Spanish Flu.

However, it’s important to get your vaccine for the flu early since it takes about two weeks for your body’s immune system to develop the necessary antibodies.

Is the Flu Shot Safe?

Yes. The flu vaccine is safe, and you cannot catch influenza from the vaccine. Any viral material in the vaccine has either been severely weakened or killed, so it does not pose a risk to your body.

However, the flu vaccine is not recommended for certain individuals, such as children under the age of six months or people who have allergies to ingredients like egg proteins. No matter how advanced vaccines will eventually become, there will always be at-risk people in our society who cannot take the vaccine themselves.

This is a big reason why herd immunity is so important. The only way to protect these individuals, such as grandparents or young children, is for everyone else to get vaccinated whenever possible.

Is the Flu Shot Effective?

Generally, yes. But the flu vaccine’s effectiveness can vary from season to season based on:

• Who is being vaccinated
• The research data available to the CDC and other organizations
• How robust or durable the year’s flu virus is – some strains are more difficult to immunize against than others

According to the CDC, some flu vaccines are not well matched to the year's circulating influenza viruses. This may cause little to no benefit from flu vaccination. On the flip side, during years when the CDC does develop an effective vaccine for circulating flu viruses, vaccinated people will experience substantial benefits and will likely not get sick from the flu at all.

Ultimately, it’s important to recognize that flu vaccines are not perfect defenses against influenza. But they are the best medical defense against circulating flu strains and all healthy individuals should look into getting vaccinated every year when possible.

How To Ease Flu Symptoms

Although it’s wise to defend yourself against getting infected by the flu in the first place, sometimes you just can’t avoid it or are unlucky. In these cases, you need to know how to ease flu symptoms so you and your child can recover more quickly.

There are two broad solutions to flu symptoms: home remedies and flu medicine. But remember that no remedy can directly treat the flu. All remedies only make your symptoms more tolerable while you wait for your immune system to tackle the infection. There are, however, prescription antiviral medications that can be used when someone has influenza, but they have to be started within the first 72 hours of being sick to be somewhat effective.

Home Remedies

It’s always smart to have a handful of home remedies ready to go when flu season rolls around. If you or your child becomes sick with the flu, you should not go to work or school and should spend time at home recovering using these remedies.

As mentioned earlier, eat plenty of healthy foods including the classic chicken soup. Chicken soup is soothing to the throat, provides you with vital vitamins and nutrients from vegetables and chicken, and ensures that you don’t become dehydrated or low on energy while your body fights off a flu virus.

Interestingly, there’s even some research showing that a bowl of chicken soup that includes vegetables may slow the movement of white blood cells in your body, helping to reduce inflammation as a result of an upper respiratory tract infection.

Besides just eating chicken soup, you should also look into drinking a variety of healthy beverages to stay hydrated. If water is too boring, consider beverages like:

• Coconut water
• Herbal tea
• Fresh juice

All of these included vitamins and minerals that your body can use to defend itself against the infection and help you maintain your strength. Herbal tea is a particularly good choice since it can include substances that have anti-inflammatory, antibacterial, and/or antiviral properties. Green and black tea are preferred over other types.

In general, you should aim to drink enough water and other fluids so that your urine is a clear or pale yellow color. Be sure to have your child drink enough water if they are infected with the flu, as kids are not always the best about hydrating themselves.

If your flu is accompanied by a sore throat and lots of mucus, try a saltwater rinse or gargle. This can soothe your throat and break up mucus, making it easier to cough up phlegm and breathe.

To make a saltwater gargle:

• Heat some water almost to a boil and allow it to cool to room temperature
• Mix one half of a teaspoon of salt in 8 ounces of warm water
• Sip the saltwater to the back of your throat and gargle it for between 10 and 30 seconds
• Spit the water into a sink and repeat another few times until comfortable
• Be sure not to swallow the water, of course.

Similarly, you can use an at-home humidifier to both soothe your sore throat, break up congestion, and make it more difficult for the flu virus to survive in your home. The flu virus typically survives longer in dry and cool indoor air. Increasing the humidity of your bedroom will make it harder for the virus to survive if it is breathed out.

By the same token, taking regular hot showers or warm baths can soothe your body and alleviate many aches and pains associated with the flu. Furthermore, breathing in warm and humid air will help to break up mucus and make it harder for the flu virus to survive outside your body, making it less likely that it will re-infect your body later.

Flu Medicine

The other big option is flu medicine or antiviral drugs. However, it’s important to only choose the correct flu medicine for your needs rather than pick the first over-the-counter remedy you find.

Why Traditional OTC Flu Remedies Have Room To Improve

In fact, traditional cold, cough, and flu medicine are usually filled with synthetic inactive ingredients and other additives, such as preservatives, flavors, and dyes.

Some adults and children may be sensitive to inactive ingredients that many OTC medications contain. Kids’ bodies are still developing, and they may not need to ingest tons of artificial dyes, and preservatives when trying to recover from the flu.

Bottom line: most traditional OTC flu medicine is packed with unnecessary ingredients.

What Are the Other Kinds of the Flu?

Alongside typical yearly flu strains, you should understand the differences between other major types of flu so you're better prepared to deal with their symptoms.

Swine Flu

The swine flu, also called H1N1, first came to the world’s attention in 2009. Swine flu still circulates throughout the population, so yearly vaccines against the seasonal flu include vaccination against the swine flu by default. However, swine flu is not particularly deadly or dangerous compared to other, more severe flu types.

Spanish Flu

The Spanish Flu was caused by a variety of H1N1 virus (the same as the swine flu) but it originated in birds. It infected around 500 million people and had very high mortality. The Spanish Flu technically ended with widespread vaccination and herd immunity. However, there are still some flu strains with genetic markers similar to the Spanish Flu.

Bird Flu

Also called H5M1, the bird flu can sometimes spread to humans although it is typically transferred from bird to bird. The last major bird flu outbreak was in 2014. Bird flu can be quite dangerous (as it’s a severe type A influenza virus), but outbreaks are not particularly common and transmission from birds to humans is rare.

The Stomach Flu

Technically, the stomach flu isn’t a type of flu at all. It’s caused by a variety of bacteria, viruses, or parasites and leads to a number of uncomfortable symptoms, such as indigestion, diarrhea, nausea, muscle aches, and more.

Depending on the source of your stomach flu, it may go away on its own or you may need to acquire antibiotics from your doctor. Symptoms may be somewhat similar to regular flu symptoms, but will be concentrated in the stomach or gastrointestinal tract.

Summary

The flu is an old virus that will likely be with us for a very long time to come. Fortunately, everyone can learn how to defend themselves against the flu and maximize their recovery time through using home remedies and real medicine, made clean.

The flu may be very uncomfortable, but its symptoms are manageable and your body should be able to fight off the infection within a week or so. It’s a good idea to make sure that both you and your children get the flu vaccine each year to reduce the likelihood of catching the flu and to increase herd immunity against the virus.