Signs and Symptoms of Mononucleosis (Mono)

Mononucleosis, or “mono,” is a highly contagious infection that is usually caused by the Epstein-Barr virus (EBV). The infection primarily affects adolescents and young adults but can occur at any age. Mono spreads through close contact with an infected person’s saliva, which is one reason mono is often referred to as the "kissing disease."

Mono symptoms typically appear within four to six weeks after you contract the virus and tend to come on gradually. It's common to experience symptoms such as fatigue, loss of appetite, and sore throat. While most people with mono feel better within six weeks, fatigue can persist for up to six months.

There are three stages of mono: prodrome, acute, and convalescent. Each stage is a different phase of the illness and presents its own set of symptoms.

Stage 1: Prodrome Stage Symptoms

The prodrome stage of mono is when symptoms begin to appear. Generally, this stage lasts for three to five days. During this stage, symptoms tend to be subtle and may include:

• Fatigue: Feeling more tired than usual
• Malaise: A general sense of discomfort or feeling unwell
• Loss of appetite: Eating less or not wanting to eat at all

Stage 2: Acute Stage Symptoms

The acute stage occurs when mono symptoms become more apparent and start to worsen. Symptoms in the acute stage last from two to six weeks and may include:

• Severe fatigue: Extreme exhaustion that makes it challenging to carry out daily activities
• Sore throat: A severe sore throat that causes dryness, itchiness, or pain
• Swollen lymph nodes: Lymph nodes in the neck and armpits that become enlarged and feel tender or sore when touched
• Fever: Having a body temperature over 99 degrees Fahrenheit, which lasts for a few days
• Enlarged tonsils: Swollen tonsils that are covered with a white-colored coating
• Headache: Persistent, dull, and throbbing head pain
• Muscle aches and weakness: Widespread muscle aches, stiffness, and feeling weak
• Rash: A non-itchy, inflamed rash on your skin that can appear pink on lighter skin tones and dark red on darker skin tones
• Respiratory symptoms: Cough, runny nose, and chest pain
• Abdominal pain: An enlarged spleen that can cause pain or discomfort in the upper left abdomen

Some people with mono may experience rare symptoms during the acute phase, including: 

• Nausea 
• Vomiting 
• Swollen eyelids 
• Bruising on the roof of the mouth 

Stage 3: Convalescent Stage Symptoms

The convalescent mono stage is the recovery phase. You enter this stage when symptoms gradually start to subside. Most people start to feel better in the convalescent stage, which lasts from four to six months. Symptoms of the final phase of mono include:

• Lingering fatigue: Fatigue may persist, but feel milder as your body recovers.
• Enlarged spleen: If your spleen is enlarged or inflamed during the recovery phase, there is still a small risk that your spleen could rupture. Avoid strenuous activity until a healthcare provider tells you it is OK to resume your normal activities or exercise routine.

Symptoms in Children

Though mono is less common in infants and young children as compared to adolescents and adults, children can still become infected with the Epstein-Barr virus and contract mono. Children who get mono often experience milder symptoms or no symptoms at all. When children do develop symptoms, they may experience:

• Fever
• Sore throat with white patches at the back of the throat 
• Swollen lymph nodes in the armpit, groin, and neck 
• Fatigue 
  

Some children can also develop less common symptoms of mono, such as:

• Headache 
• Chills
• Decreased appetite 
• Swollen eyelids
• Sensitivity to light 
• Anemia

When to See a Healthcare Provider 

While most cases of mono resolve on their own with time and rest, certain symptoms may warrant a trip to your healthcare provider. You should reach out to your healthcare provider if you or your child have:

• Symptoms that persist for ten or more days 
• Weakness in your arms
• Severe headache or body aches 
  

It's important to note that some symptoms warrant immediate medical attention. This may indicate that you have a ruptured spleen or other mono complications. It's vital to seek prompt medical care if you or your child experience any of the following: 

• Sharp pain in the upper left abdomen 
• Confusion
• Fainting
• Blurry vision 
• Difficulty breathing
• Persistently high fever
• Trouble swallowing food
• Yellowing of the eyes or skin (jaundice) 
• Extreme weakness in your arms or legs
  

A Quick Review 

Mononucleosis, or “mono,” is a highly contagious virus usually caused by the Epstein-Barr virus (EBV). Mono most commonly affects adolescents and young adults but can occur at any age. Classic mono symptoms include fatigue, sore throat, malaise, swollen lymph nodes, and loss of appetite. Less common symptoms can include headache, fever, rash, and abdominal pain. 

Mono progresses through three distinct phases. The prodrome stage has mild symptoms, such as fatigue and decreased appetite. The acute stage is when classic mono symptoms develop, persisting for up to six weeks. The convalescent stage is the recovery phase when most symptoms go away, and may last for up to six months.

Not everyone with mono will experience every symptom, and symptoms can come and go throughout the course of the illness. Trust your instincts and seek medical care if you have concerns about the severity or progression of your symptoms. Your healthcare provider can provide a diagnosis and offer treatment options that are right for you.