Signs of Mono: Extreme Fatigue Is Just One of Them

Jaundice mono enlarged liver hepatomegaly
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Mono, short for infectious mononucleosis, is a common viral illness that often affects adolescents and young adults. Mono—also as the kissing disease—can cause swollen glands, tiredness, a sore throat, and other symptoms. According to the Centers for Disease Control and Prevention (CDC), it's usually caused by the Epstein-Barr virus (EBV), though other viruses can be culprits, too.

EBV is one of the most common human viruses found around the world and is a member of the herpes family, according to the CDC. Roughly 90% of adults have antibodies against EBV in their blood, which means they were exposed to the virus years earlier, most likely during childhood.

EBV and other viruses that can cause mono like to hitch a ride in people's saliva, which spreads the virus through kissing, and sharing cups and utensils. These viruses can also be spread in other bodily fluids, including blood and semen, according to the CDC.

"You can pass it on when you have direct sharing of secretions," Christina Hermos, MD, assistant professor at the University of Massachusetts Medical School and pediatric infectious disease specialist at the UMass Memorial Children's Medical Center, told Health.

Thankfully, mono is less contagious than the common cold. People with mono don't usually have coughing or sneezing, so they're not spraying virus-containing droplets of saliva into the air, said Dr. Hermos.

If you come into contact with the virus that causes mono, the CDC says it can take four to six weeks after you've been infected for symptoms to appear—and they may not arrive all at once. Many people start to feel better two to four weeks after that, but fatigue can persist for many weeks or even months.

What Are the Symptoms?

Classic signs of mono include fever, sore throat, swollen lymph nodes (commonly called swollen glands), and fatigue. According to the CDC, healthcare providers often diagnose mono based on a patient's symptoms and physical exam results. If there is any question, though, blood tests are ordered to confirm the diagnosis or rule out other causes.

According to the CDC, someone who has mono will most likely show a higher white blood cell count (white blood cells help fight off infection); some unusual-looking white blood cells; fewer than normal other blood cells, including platelets and neutrophils; and abnormal liver function.

Here's a closer look at each symptom of mono.


Fatigue is one of the most common symptoms of mono. But not just any fatigue. Mono tiredness tends to be extreme, according to Johns Hopkins Medicine. If the exhaustion is accompanied by other symptoms or if it persists, see your healthcare provider.

Feelings of fatigue typically resolve within several weeks to a few months, according to John Hopkins Medicine.

Sore Throat

Mono can sometimes be confused with strep throat, a painful bacterial infection of the throat.

With mono, your throat can be severely sore or itchy, and some people have difficulty swallowing, said Sherly Mathew, MD, an internal medicine physician with Health Quest Medical Practice in Hyde Park, New York.

Dr. Mathew noted that it's not uncommon to see white patches on patients' tonsils. And "sometimes you will see a little bit of rash inside the mouth on the upper palate."

Swollen Glands

According to the National Library of Medicine MedlinePlus resource, while they're commonly called "swollen glands," the correct terminology is lymphadenopathy, which means "swollen lymph nodes." Lymph nodes help fight off an infection. Consequently, they may swell up when you have mono. Lymph nodes are found throughout the body, but with mono, you're most likely to notice swollen them in your neck.

Fever or Chills

People with mono usually have a fever, ranging from 102 to 104 degrees Fahrenheit, said Dr. Mathew.

A lot of patients say their fevers peak in the afternoon or evening, "and that could continue for a few days to weeks, depending on how they fight the infection," added Dr. Mathew.

Chills, in response to the fever, are also common.

Headache or Muscle Aches

Mono can lead to any number of vague symptoms, such as headaches or muscle pains, perhaps sparked by other discomforts.

"Anyone with fever and fatigue will have [a] headache," said Dr. Mathew.

Skin Rash

A pink or red splotchy or measles-type skin rash is a less common sign of mono.

While antibiotics are not used to treat mono, "some people test positive for strep when they have the Epstein-Barr virus," explained Dr. Hermos. When they take antibiotics for the strep infection, they may break out in a rash as a reaction to the antibiotics. "That's another clue you could have EBV," said Dr. Hermos.

Swollen Spleen or Sore Upper Abdomen

The spleen is a blood-filtering organ that plays a role in fighting infections. Though a less common symptom, when you have mono, it can become inflamed and enlarged, according to the CDC.

Consequently, you may feel some tenderness when your healthcare provider presses on the upper left part of your abdomen.

The CDC advises against participating in contact sports until you're fully recovered, as any trauma to the abdomen can cause your swollen spleen to rupture. If you have sudden, sharp abdominal pain, seek emergency medical treatment.

It's important to note that the CDC also states if the liver or spleen did become inflamed during mono, they can remain enlarged even after the mono fatigue ends. If you plan on doing any type of contact sport or activity that risks falling after your other symptoms have subsided, it's wise to get cleared by your healthcare provider first.


People with mono can develop jaundice, a yellowing of the eyes or skin due to a problem with the liver. Jaundice suggests that the liver is enlarged, a condition called hepatomegaly, which can be a complication of mono, explained Dr. Mathew.

According to a 2020 study in the journal Clinical Practices and Cases in Emergency Medicine, jaundice associated with mono is a rare complication. Sometimes, though, the whites of the eyes may become tinged with yellow, a sign of jaundice, said Dr. Hermos.

Jaundice can also be a complication of other diseases, so if you have yellowing of the skin or eyes, with or without other symptoms, visit your healthcare provider for an evaluation.

How Is Mono Treated? Can It Be Serious?

Serious complications can occur but are rare, according to the National Library of Medicine MedlinePlus resource. Most people recover with the recommended treatment of rest, hydration, and over-the-counter pain relievers as needed.

If you think you may have mono, give your healthcare provider a call. It's best to confirm the diagnosis and have medical support in the event that yours becomes a serious case.

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