What Is Mono (Mononucleosis)?

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Infectious mononucleosis, or mono, is a contagious viral illness typically caused by the Epstein-Barr virus (EBV), which spreads via bodily fluids and saliva. Although mononucleosis is contagious, EBV isn't as contagious as some other airborne viruses, such as rhinoviruses, that spread through the air and cause the common cold.

Mono is called "the kissing disease" because kissing is the leading cause of Epstein-Barr virus infection among adolescents and young adults. However, mono-causing EBV can also spread through saliva-contaminated food utensils, used straws, and shared drinking glasses or toothbrushes. Roughly 1 in 4 teens and young adults exposed to EBV develop a case of mono.

Read on to learn about mononucleosis (mono) diagnosis, what "mono rash" looks like, the three stages of mono, how long mono lasts, if it requires quarantine, and more.

Tired teen sick on the couch

Rebecca Smith / Getty Images

What Causes Mono (Mononucleosis)?

Most mono cases are caused by Epstein-Barr virus (EBV). Epstein-Barr virus has a surprisingly long incubation period, between four and eight weeks. On average, it lasts six weeks. Because of this lengthy incubation period, it takes over a month for someone infected with mono-causing EBV to start noticing mononucleosis symptoms.

How Is Mono Spread?

The Epstein-Barr virus that causes mono primarily spreads via saliva. Contagious levels of the Epstein-Barr virus in saliva are replaced constantly and can fill the mouth between swallows in two minutes or less.

Because EBV particles constantly shed into saliva, anything that comes in contact with a contagious person's saliva (e.g., toothbrush, food utensil, straw) becomes contaminated with the Epstein-Barr virus. This mono-causing virus spreads when people borrow toothbrushes, share food utensils, smoke the same cigarette, take a sip from someone else's drinking glass, or use the same straw.

Although objects that come in contact with a contagious person's EBV-filled saliva can pass infectious mononucleosis, kissing is the most common way mono spreads among teens and young adults.

Mono Symptoms

People with mono typically feel very tired or fatigued. In addition to lethargy (lack of energy), headaches, and body aches, infectious mononucleosis (mono) is characterized by these three clinical symptoms:

Infectious mononucleosis can also cause "mono rash." The skin rash associated with mono varies from person to person. It can look like a  maculopapular, or morbilliform, rash, similar to a measles rash, with flat spots and bumps on the skin. Sometimes, mono rash resembles hives (urticaria) or pinpoint-sized red, brown, or purple spots called petechiae.

What Are the Stages of Mono?

After an incubation period that averages about six weeks, the Epstein-Barr virus that causes mono starts to cause noticeable symptoms that progress in these three stages:

  • The prodrome stage is a period of about three to five days when mild mono symptoms start to appear.
  • The acute phase is a period of about two to six weeks when mono symptoms are most severe.
  • The convalescent stage is the three- to six-month recovery period when symptoms slowly regress.

How Is Mono Diagnosed?

Mono is diagnosed by a healthcare provider asking questions about a patient's symptoms and performing a physical exam. The following blood tests are also used to diagnose mono:

  • EBV antibody test: A blood test that detects EBV antibodies indicating the presence of mono
  • White blood cell (WBC) tests: Blood tests that count white blood cells like lymphocytes and monocytes, looking for high monocyte levels and lymphocytes that are associated with mononucleosis

Mononucleosis Treatment

Because it's a virus that causes infectious mononucleosis, it won't respond to antibiotic treatment, which only works on diseases caused by bacteria. Because there isn't a specific treatment for mono, the best way to care for mono is to get plenty of rest, practice stress relief strategies, stay hydrated, and eat healthy foods.

Secondary Mono Complications

Very rarely, infectious mononucleosis leads to secondary mono complications such as:

When to See a Healthcare Provider

Splenic rupture with mono is rare, but if you have mono symptoms and experience a sudden, sharp pain on the upper left side of your abdomen, contact a healthcare provider and seek medical attention immediately.

How Long Does Mono Last?

From start to finish, mono lasts for months. After an incubation period of about six weeks, if you're infected with the Epstein-Barr virus and develop mono, you will start to experience symptoms that typically progress and regress in three stages over the next six months.

The prodrome stage of mono, when mild symptoms start to appear, can last three to five days. The acute phase, when symptoms are most severe, can last two to six weeks. The convalescent stage, when mono symptoms regress and you start to feel better, can last three to six months.

Can You Get Mono More Than Once?

Most people only get mono once. However, it's possible to have recurrent mononucleosis symptoms if the Epstein-Barr virus that causes mono stays active in a person's body. Mono that you get more than once or recurrently is called chronic mono or chronic active Epstein-Barr virus infection (CAEBV).

 Is Mono Contagious?

Mono is a highly contagious viral disease. The Epstein-Barr virus that causes mononucleosis is one of the world's most common and contagious viruses. It's estimated that 95% of the adult population has been infected with EBV. Many people are exposed to EBV during childhood and develop immunity before their teenage years, which makes them less likely to get mono in high school or college.

If you don't catch the Epstein-Barr virus at a young age, however, you are more likely to develop mono as a teen or young adult if you start having intimate contact with romantic partners. Also, sharing personal items that touch people's lips and mouths (e.g., straws, water bottles, cigarettes) spreads contagious saliva-based germs.

Because the mono-causing virus spreads via bodily fluids and saliva, kissing and other forms of intimate contact make high school and college students particularly vulnerable to catching mono for the first time. That said, mono isn't as contagious as other viruses that spread more readily through the air.

 Do You Need to Quarantine for Mono?

Strict quarantines aren't necessary for people with mono, but there are steps everyone can take to help prevent the transmission of mononucleosis. These include:

  • Washing your hands regularly
  • Social distancing from people with mono
  • Avoiding kissing people if you're feeling sick
  • Thoroughly cleaning saliva off food utensils, drinking glasses, and children's toys
  • Not sharing anything that touches people's lips, like cigarettes or water bottles
  • Using a condom to avoid transmission of EBV via ejaculate fluids

Recovery and Outlook

While recovery from mono usually takes months, the long-term outlook for most cases of infectious mononucleosis is good. The majority of people who catch "the kissing disease" don't experience secondary complications and make a full recovery.


Infectious mononucleosis, or mono, is a viral illness that typically spreads via saliva and is caused by the Epstein-Barr virus (EBV). Mononucleosis is nicknamed "the kissing disease" because most teens and young adults catch mono-causing EBV from kissing. It can also spread when personal items that come in contact with saliva are shared.

A full recovery from mono can take upwards of six months, but the most severe symptoms, experienced during the acute phase, typically last two to six weeks. These symptoms include extreme fatigue, headaches, body aches, fever, sore throat, and swollen lymph nodes. Sometimes, people with mono experience an enlarged spleen or so-called mono rash.

Most people only get mono once during adolescence or young adulthood, but in rare cases, EBV stays active and causes recurrent, chronic mono. People who develop mono can be contagious for a few weeks before they feel sick until a few months after their severe symptoms subside.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Christopher Bergland
Christopher Bergland is a retired ultra-endurance athlete turned medical writer and science reporter.