Mononucleosis (glandular fever) (2025)

Mono is most often caused by the Epstein-Barr virus (EBV). This virus belongs to the Herpes viridae family, but mononucleosis is not a herpes infection. Mono infection is extremely common – most people will get infected with EBV at some point in their lives, often in childhood, without even realizing it because symptoms can be very mild. However, when teens or young adults get infected for the first time, they are more likely to develop the classic symptoms of mono.

You mainly get mono through direct contact with the saliva of someone who has the virus. That's why it's nicknamed the kissing disease. It’s also transmitted by sharing things that touch the mouth, like drinks, eating utensils, toothbrushes or lip balm. Less commonly, it might spread through droplets from a cough or sneeze, or through blood or semen. Because the virus can stay in someone's saliva for months after they feel better, it's easy to spread without knowing it. Many people carry EBV without symptoms and can still pass it on.

Preventing mononucleosis can be tricky because the virus that usually causes it, Epstein-Barr virus, is very common and spreads easily through saliva. Many people carry EBV without even knowing it and can pass it on. However, you can take steps to lower your chances of catching it, especially from someone you know is sick.

Since mono spreads through saliva, the best prevention is to avoid contact with an infected person's saliva. This means:

• don't share drinks: avoid sipping from the same cup, water bottle or can;
• don't share utensils: use your own forks, spoons and knives;
• don't share personal items: things like toothbrushes or lip balm can transfer the virus; and
• avoid close contact: since it's called the kissing disease, avoid kissing someone who has mono (or has recently recovered, as the virus stays in saliva for weeks to months).

While washing your hands regularly is good hygiene for preventing many illnesses, it's less effective against mono since it's not typically spread through hands. Focusing on not sharing items that touch the mouth is the most direct way to reduce your risk of getting mono.

Mono symptoms can feel a lot like a bad case of the flu, but they tend to last longer. The most common signs usually show up about 4 to 6 weeks after you get infected and include:

• severe sore throat: it might hurt a lot to swallow, and your throat might look very red
• fever: usually between 38.3 °C to 40 °C
• swollen lymph nodes: you might feel lumps in your neck, armpits or groin area
• swollen tonsils: they might look red and large, sometimes with white or yellowish patches on them
• headache and body aches: similar to what you might feel with the flu
• extreme fatigue: feeling tired all the time, even after having a good amount of sleep
• loss of appetite.

Some people might also get a rash or have a swollen spleen or liver, but these are less common. Symptoms often develop slowly and might not all appear at once.

How long mono lasts can vary quite a bit from person to person. Most of the main symptoms, like the fever and severe sore throat, usually start getting better within a couple of weeks. However, the swollen lymph nodes and tonsils might take a bit longer to go back to normal size, sometimes up to 4 weeks.

The biggest issue for many people is the fatigue. The feeling of being extremely tired can linger for several weeks up to a few months after the other symptoms have gone away. This is why getting plenty of rest is so important when you have mono. Trying to push through the tiredness can sometimes make it last longer. Gradually increasing your activity level as you start to feel better is usually the best approach.

Yes, mono is contagious. As mentioned earlier, it spreads mainly through saliva. You are most contagious while you have symptoms like fever, but the Epstein-Barr virus can remain active in your saliva for a long time after your symptoms disappear – potentially for 6 months or even longer.

Most people get infected with EBV and have no symptoms at all, or only very mild ones they mistake for a cold. These people can still carry the virus in their saliva and spread it to others without ever knowing they had mono. This is one reason why EBV is so widespread. To be safe, even after you feel better from mono, it's a good idea to avoid sharing drinks, utensils and toothbrushes, and avoid kissing people for a few months to reduce the chance of spreading it.

Doctors can often make a diagnosis just based on your typical symptoms and a physical exam. If your doctor thinks you might have mono based on your symptoms (like severe fatigue, sore throat, fever and swollen lymph nodes), they might order a blood test to help confirm it. The most common test is called the monospot test (or heterophile antibody test). This test looks for specific antibodies (proteins your immune system makes to fight infection) that often show up in your blood when you have mono.

However, the monospot test isn't perfect. It might come back negative early in the illness (especially in the first week or two), even if you do have mono. Sometimes, doctors might repeat the test later if symptoms continue. In other cases, especially if the monospot is negative but mono is still suspected, doctors might order different blood tests that look specifically for antibodies against the Epstein-Barr virus. These tests are more specific and can help tell if you have a current, recent or past EBV infection.

Since mono is caused by a virus (usually EBV), antibiotics won't help – they only work against bacteria.

There isn't a specific medicine that cures mono. The treatment focuses on relieving your symptoms and helping your body fight off the infection. This is called supportive care.

These are most important things you can do:

• Get plenty of rest. Your body needs energy to recover, and the fatigue can be intense. You might need to stay home from school or work and avoid sports for several weeks.
• Drink lots of fluids. Water, juice and broth help prevent dehydration and can soothe a sore throat.
• Relieve pain and fever. Over-the-counter pain relievers like acetaminophen (paracetamol) or ibuprofen can help with fever, sore throat and body aches. Avoid giving aspirin to teens due to the risk of Reye's syndrome, a rare but serious condition.
• Soothe your sore throat. Gargling with salt water (one quarter to one half teaspoon of salt in a glass of warm water) or using throat lozenges or sprays can help.

It's also crucial to avoid contact sports or heavy lifting for at least 3–4 weeks, even if you feel better, because mono can cause your spleen to swell, making it fragile and at risk of rupturing, which is a medical emergency. Always follow your doctor's advice on when it's safe to return to normal activities.

Yes, mono commonly affects the tonsils. Swollen, inflamed tonsils are one of the classic signs of the illness. When you have mono, your tonsils can become quite enlarged and red. Often, they develop white or yellowish patches or a coating on their surface – this is called exudate. This swelling and coating contribute significantly to the severe sore throat and difficulty swallowing that many people with mono experience.

In some cases, the tonsils can swell so much that they almost touch each other in the back of the throat (sometimes called kissing tonsils). This can make breathing feel a bit difficult, although serious breathing problems are rare. The swelling and soreness in the tonsils usually get better along with the other main symptoms like fever, typically within a couple of weeks, but sometimes it can take a bit longer for them to return completely to their normal size. Using salt water gargles and pain relievers can help manage the discomfort.

Mono can sometimes cause a skin rash, although it's not one of the most common symptoms like fatigue or sore throat. If a rash does occur with mono itself, it often looks like faint, flat pink or reddish spots spread across the body (a nonspecific maculopapular rash). It usually doesn't itch very much.

However, a more common reason people with mono get a rash is if they are mistakenly given certain antibiotics, particularly ampicillin or amoxicillin. These antibiotics are often prescribed for bacterial throat infections like strep throat. If someone actually has mono (which is viral) and takes one of these specific antibiotics, they are very likely (up to 90% of the time) to develop a widespread, often itchy, red rash. This reaction doesn't mean they are allergic to the antibiotic in general; it's a specific reaction that happens when these drugs interact with the mono infection. This is one reason why it's important for doctors to consider mono if you have a severe sore throat before prescribing antibiotics.

Global HIV, Hepatitis and STIs Programmes (HHS)