• Posted February 2, 2026

Infectious Mononucleosis: What It Is, Symptoms, Causes, Diagnosis, Treatment and More

Infectious mononucleosis, often called “mono,” is a viral illness best known for causing extreme fatigue, sore throat and swollen glands.

Mono is often referred to as the “kissing disease,” because it spreads through saliva, but that is only one way it can pass from person to person.

Mono is common in teens and young adults, but people of all ages may get it. While most recover fully, symptoms may last for weeks and sometimes longer.

Infectious mononucleosis is most often caused by the Epstein-Barr virus (EBV), a member of the herpes virus family. Less common mono-like illnesses may be caused by other viruses, such as cytomegalovirus (CMV), human immunodeficiency virus (HIV) or hepatitis viruses.

Once infected with EBV, the virus remains in the body for life, even though symptoms usually resolve.

Most people are infected with EBV at some point, often during childhood when symptoms are mild or absent, according to the National Institutes of Health (NIH). When infection happens during adolescence or young adulthood, mono is more likely to develop.

What are the Symptoms of Infectious Mononucleosis?

Symptoms usually appear four  to six weeks after exposure and may include:

• Extreme fatigue

• Sore throat

• Fever

• Swollen lymph nodes in the neck and armpits

• Swollen tonsils

• Headache

• Muscle aches

• Loss of appetite

• Skin rash

• Enlarged spleen or liver in some people

Fatigue may last longer than other symptoms and sometimes persists for several weeks or months.

How is Infectious Mononucleosis Diagnosed

Doctors usually diagnose mono based on symptoms and a physical exam, along with blood tests. Diagnosis may include:

Physical exam. The doctor may check for swollen lymph nodes, tonsils, liver or spleen.

Blood tests. These may include:

• A heterophile antibody test, often called a Monospot test

• Tests for antibodies to Epstein-Barr virus

• A complete blood count showing abnormal white blood cells

Early testing may be negative, so repeat testing is sometimes needed if symptoms strongly suggest mono, according to the U.S. Centers for Disease Control and Prevention (CDC).

How is Infectious Mononucleosis Treated?

There is no specific cure for mono because it is caused by a virus. Treatment focuses on relieving symptoms and supporting the body’s recovery.

Treatment may include:

Rest. Fatigue is a major symptom, so listening to your body and resting is essential.

Fluids. Drinking plenty of fluids helps prevent dehydration.

Fever and pain control. Acetaminophen or ibuprofen may reduce fever and body aches.

Throat comfort. Saltwater gargles, warm liquids and lozenges may help soothe a sore throat.

Avoiding contact sports. If the spleen is enlarged, contact sports should be avoided for at least three to four weeks or until the patient is leared by a doctor, because of the risk of spleen rupture

Antibiotics do not treat mono. In fact, giving certain antibiotics like amoxicillin to someone with mono often causes a rash, which may help clue doctors into the diagnosis.

Some ways it is spread include:

• Sharing drinks or utensils

• Kissing

• Coughing or sneezing

• Blood or sexual contact, less commonly

Once infected, a person may spread the virus for weeks, even if they feel better.

What Factors Put People at Risk?

Certain factors increase the likelihood of getting mono, including:

Age: Teens and young adults are most likely to develop symptoms.

Close contact: Sharing drinks, utensils or kissing increases exposure.

Weakened immune system: People with immune system conditions may be more vulnerable.

Crowded living situations: Dorms and camps increase the risk of disease transmission.

What Can Patients Expect While Living With Infectious Mononucleosis?

Most people recover fully, but mono may require patience during recovery.

Short-term complications may include severe throat swelling, dehydration and secondary infections such as strep throat.

Rare but serious complications may include ruptured spleen, liver inflammation, low blood cell counts and heart or nervous system involvement, according to the Mayo Clinic and NIH. These are uncommon but require prompt medical attention.

When Should People Seek Medical Care?

You should contact a doctor if you or your child has:

• Severe abdominal pain or pain in the left upper abdomen

• Trouble breathing or swallowing

• Yellowing of the skin or eyes

• Persistent high fever

• Symptoms lasting longer than expected

What Can People Do to Prevent Infectious Mononucleosis?

There is no vaccine for EBV, but risk may be reduced by:

• Avoiding sharing drinks or utensils.

• Not kissing someone who is ill.

• Practicing good hand hygiene such as washing your hands frequently with soap and water or using hand sanitizer when soap and water aren’t available.

Because EBV is widespread, complete prevention is difficult.

About the expert

Dr. Sarah Adams is a retired primary care pediatrician and nationally recognized child health expert, media spokesperson and advocate. She serves in leadership roles with the Ohio Chapter of the American Academy of Pediatrics and the National AAP, focusing on nutrition, digital wellness, communication and family health education. Dr. Adams hosts the podcast “Growing Up with Dr. Sarah” and regularly contributes to national health outlets.