Mono is a viral infection that causes symptoms like fatigue, swollen glands, and a severe sore throat. It’s hard to say exactly how long the infection is contagious. Even researchers aren’t totally sure.

After you contract the Epstein-Barr virus (EBV) — the main virus that causes mono — it begins to reproduce in your throat. That means you can pass the virus to other people who come in contact with your saliva, so you have to be careful about kissing or sharing personal items like cups or utensils.

However, you may not realize you’re sick during this time. It can take 4–6 weeks from when you first contract the virus for symptoms like fatigue, a sore throat, and muscle aches to appear. This is called the incubation period.

Once your symptoms do appear, they may last for 2–4 weeks.

You can pass the virus to other people for anywhere from 3 months to over a year after your symptoms subside.

EBV is commonly passed via saliva, which is why mono is often called the “kissing disease.” However, it can also be passed via other bodily fluids, including blood and semen.

If you kiss a person who has the virus (or you share personal items like utensils, glasses, food, or lip balm), you can develop the infection. You can also develop mono if someone who’s sick with mono coughs or sneezes close to you.

Teens and young adults are most likely to get sick with mono.

To avoid getting mono yourself, follow these tips:

  • Avoid close contact with anyone that you know has mono.
  • Don’t kiss or share personal items like toothbrushes, utensils, food, straws, or glasses with anyone that you suspect has mono.
  • Care for your overall health by eating a nutritious diet, exercising daily, and sleeping for at least 6–8 hours nightly.
  • Wash your hands regularly.

To avoid spreading the virus if you have mono, follow these tips:

  • Stay home and rest until your symptoms improve.
  • Don’t kiss or share any personal items — including utensils, glasses, lipstick, and food — with other people.
  • Ask your doctor if you should use a condom when you have sex and for how long. EBV can spread through semen during sexual contact.
  • Wash your hands regularly.

If you’ve developed mono, you typically have symptoms like:

  • fatigue
  • a sore throat
  • fever
  • swollen lymph nodes in your neck
  • headache
  • muscle aches

If your symptoms worsen or persist for more than a day or two, make an appointment to see your doctor. They can determine what’s causing your symptoms and advise you on any next steps.