Mumps is caused by a virus that spreads through saliva and respiratory droplets

Mumps comes from infection with the mumps virus, a pathogen that travels from person to person through the air. When someone with mumps coughs, sneezes, or talks, they release tiny droplets containing the virus. Anyone nearby who breathes in those droplets can become infected. The virus can also spread if you touch a contaminated surface and then touch your mouth, nose, or eyes.

The mumps virus belongs to a family called paramyxoviruses. Once it enters your body, it travels to your salivary glands — the glands in your cheeks and under your jaw that produce saliva. The virus multiplies there, causing the swelling and pain that mumps is known for. It can also spread to other parts of your body, including the brain, pancreas, and reproductive organs.

Key Takeaways

  • Mumps spreads through respiratory droplets when an infected person coughs, sneezes, or talks, or through contact with contaminated surfaces.
  • The mumps virus attacks the salivary glands first, which is why swollen cheeks and jaw pain are the hallmark symptoms.
  • You are most contagious starting a few days before symptoms appear and continuing for about five days after the swelling starts.
  • The MMR vaccine prevents mumps in most people who receive it, which is why mumps is now rare in countries with high vaccination rates.
  • People without immunity — either from vaccination or past infection — are at risk if exposed to someone carrying the virus.

How the virus enters and spreads through your body

The mumps virus enters through your respiratory tract — your nose, mouth, and throat. From there, it travels to your salivary glands and begins to multiply. The infection causes inflammation and swelling in these glands, which is why your cheeks puff up and become tender. Some people also develop fever, headache, and body aches as their immune system fights the infection.

In some cases, the virus spreads beyond the salivary glands to other organs. It can reach the brain and cause meningitis (inflammation of the membranes around the brain and spinal cord), the pancreas and cause pancreatitis, or the testicles or ovaries and cause inflammation there. These complications are less common but can be serious, especially in adults.

Who is most likely to catch mumps

People without immunity to mumps are at risk of infection if exposed to the virus. Immunity comes from two sources: the MMR (measles, mumps, rubella) vaccine or a past infection with mumps. The MMR vaccine is given in two doses, usually starting at age 12 months. If you received both doses, your protection is strong. If you received only one dose or none, your risk is higher.

Unvaccinated people, people who received only one dose of the vaccine, and people born before the vaccine was widely used may have no immunity. Infants too young for vaccination and people with certain medical conditions that weaken the immune system are also at higher risk. In outbreaks, mumps spreads most easily in crowded settings like schools, dormitories, and workplaces where people spend time together indoors.

Why mumps is rare in vaccinated populations

The MMR vaccine is highly effective at preventing mumps. Studies show that two doses prevent mumps in about 88 percent of people who receive them. This high rate of protection means that in countries where most people are vaccinated, the virus has few hosts and cannot spread easily. When vaccination rates drop, mumps can resurface in communities.

Outbreaks in recent years have occurred in pockets of unvaccinated or under-vaccinated people. These outbreaks show that mumps has not disappeared — it is simply held in check by widespread immunity. If vaccination rates fall significantly, mumps could become common again, as it was before the vaccine became available in the 1970s.

The contagious period and how long you can spread it

A person with mumps is contagious starting about two days before symptoms appear and continuing for about five days after the swelling begins. This means you can spread mumps to others even before you know you have it. The virus is present in saliva during this entire window, which is why respiratory droplets are the main route of transmission.

After five days of swelling, the risk of spreading mumps drops significantly. However, the virus may still be present in saliva for a longer period. If you have mumps, staying home and avoiding close contact with others during the first five days of illness is the most effective way to prevent spread.

Why some vaccinated people still get mumps

Vaccine breakthrough — mumps in someone who was vaccinated — does happen, though it is uncommon. The MMR vaccine is not 100 percent effective. About 12 percent of people who receive two doses may still develop mumps if exposed to the virus. Breakthrough cases tend to be milder than mumps in unvaccinated people, with less severe swelling and fewer complications.

Breakthrough cases are more likely in people who received only one dose of the vaccine or who were vaccinated many years ago. Immunity can wane over time, though this is not common. If you are unsure whether you were vaccinated or how many doses you received, your doctor can check your vaccination records or test your immunity level.

Other factors that increase your risk

Age matters: mumps is more common in children and young adults, though anyone without immunity can catch it. Adults who develop mumps often have more severe symptoms and higher rates of complications than children. Pregnancy is also a risk factor — pregnant people who catch mumps face higher rates of miscarriage, though mumps does not cause birth defects.

Certain medical conditions weaken your immune system and make mumps more likely to spread through your body and cause complications. These include HIV, cancer, and conditions treated with immunosuppressive medications. If you have a weakened immune system and are unsure about your mumps immunity, talk to your doctor about whether the MMR vaccine is right for you.

Frequently Asked Questions

Can you catch mumps twice?

Mumps infection usually provides lifelong immunity, so catching it twice is rare. However, reinfection is possible, especially if your first infection was mild or if your immune system did not respond fully. Most people who have had mumps once are protected for life.

Is mumps contagious before symptoms show up?

Yes. You can spread mumps to others starting about two days before swelling appears. This is why mumps spreads easily in communities — people do not know they have it and continue their normal activities, exposing others to the virus.

Can you get mumps from someone who is vaccinated?

It is unlikely but possible. Vaccinated people who develop breakthrough mumps can still spread the virus, though they are usually contagious for a shorter time and shed less virus than unvaccinated people. The risk of transmission from a vaccinated person is lower than from an unvaccinated person.

Does the MMR vaccine contain the live mumps virus?

The MMR vaccine contains a weakened (attenuated) form of the mumps virus, not the full-strength virus. This weakened virus trains your immune system to recognize and fight mumps without causing the disease. You cannot catch mumps from the vaccine itself.

Why do some people get mumps even though mumps is supposed to be rare?

Mumps still occurs in areas where vaccination rates are lower or in people who were not vaccinated. It also spreads in crowded settings where unvaccinated people spend time together. Outbreaks can happen quickly in these pockets, even though mumps is rare overall in vaccinated populations.