Skip to content
Know.itKnow.it
Create an animated lesson
On request

This article is free to read. Creating a lesson uses your daily or stored credits; review the language and settings before starting.

How do viruses spread?

Medicine & HealthLesson on requestFree to readयह पेज हिंदी में पढ़ें

Quick answer

Viruses spread mainly through the air when an infected person exhales, talks, coughs or sneezes, releasing droplets and aerosols that others inhale or that land on their eyes, nose or mouth. They can also spread by touching contaminated surfaces, through blood or sexual contact, or from mother to child.

Viruses spread when an infected person expels virus-laden droplets or aerosols that reach another person's eyes, nose or mouth, or when those particles contaminate surfaces that others touch before touching their face. Some viruses also pass through blood, sexual contact, or from mother to child.

Step by step

  1. An infected person exhales, speaks, coughs or sneezes, releasing virus particles inside respiratory droplets and aerosols.
  2. Larger droplets fall to the ground within a metre or two, while smaller aerosols can remain suspended and drift further.
  3. A susceptible person inhales the aerosols or gets droplets on their eyes, nose or mouth, where the virus can enter cells.
  4. Alternatively, contaminated hands touch a surface and then the face, transferring virus particles to mucous membranes.
  5. Once inside, the virus hijacks the person's cells to make copies of itself, sometimes before any symptoms appear.
  6. The newly infected person then exhales or touches others, continuing the chain of transmission.

Key things to understand

  1. An infected person releases virus particles in droplets and tiny aerosols when they cough, sneeze, talk or breathe.
  2. Larger droplets fall to the ground quickly, while smaller aerosols can stay airborne and travel further.
  3. A new person becomes infected when virus particles land on mucous membranes in the eyes, nose or mouth, or are inhaled.
  4. Some viruses spread indirectly when contaminated hands touch a surface and then the face, or via shared objects.
  5. Other viruses spread through blood, sexual fluids, or from mother to child during pregnancy, birth or breastfeeding.

Labelled diagram

  1. Source

    An infected person exhales, talks, coughs or sneezes, releasing droplets and aerosols containing virus particles.

  2. Airborne

    Larger droplets fall quickly, but smaller aerosols can stay suspended and travel through indoor air.

  3. Entry

    A nearby person inhales the aerosols or gets droplets on their eyes, nose or mouth.

  4. Infection

    The virus enters cells, makes copies of itself, and the new person can then spread it onward.

How a respiratory virus spreads from person to person

Real-world examples

  • A person with a cold talks in a crowded room, and tiny aerosols carrying rhinovirus are inhaled by someone standing two metres away.
  • A child with norovirus vomits on a bathroom floor; virus particles land on a tap handle and infect the next person who touches it.
  • A healthcare worker receives a needlestick injury from a patient with hepatitis B, allowing the virus to enter through the bloodstream.
  • A pregnant woman with HIV can pass the virus to her baby during childbirth or breastfeeding without treatment to suppress the virus.

Common mistake

✗ Myth: You can only catch a virus from someone who is visibly sick.

✓ Fact: Many viruses spread from people who have no symptoms yet, or who never develop symptoms at all. This silent transmission is why outbreaks can grow even when everyone feels fine.

People also ask

How do viruses spread from person to person?
Respiratory viruses spread mainly through the air when an infected person exhales, talks, coughs or sneezes, releasing droplets and aerosols that others inhale or that land on their eyes, nose or mouth. Some viruses also spread by touching contaminated surfaces, through blood or sexual contact, or from mother to child.
Can you catch a virus from touching a surface?
Yes, for many viruses. When an infected person coughs or touches their face, they can leave virus particles on doorknobs, handrails or phones. If you touch that surface and then your eyes, nose or mouth, the virus can enter your body. Handwashing reduces this risk.
How long are you contagious with a virus?
It depends on the virus. Some, like the common cold, are most contagious for a few days around symptom onset. Others, such as influenza, can be spread from one day before symptoms start. Some viruses, like norovirus, remain contagious for days after you feel better.
Can you spread a virus before you feel sick?
Yes, for many respiratory viruses. People can shed virus particles for one to two days before symptoms appear, and some infections produce no symptoms at all. This presymptomatic and asymptomatic spread makes it hard to contain outbreaks by isolating only those who feel ill.
How long do viruses survive on surfaces?
It varies widely by virus and surface. Some enveloped viruses survive only hours on cardboard or copper, while others can remain infectious for days on stainless steel or plastic. Survival also depends on temperature, humidity and sunlight, so no single rule covers all viruses.
Why do some viruses spread more easily than others?
Spread depends on how much virus an infected person releases, how long they remain infectious, and how well the virus survives in air or on surfaces. Viruses that spread through the air in tiny aerosols can infect many people in a crowded indoor space, while those requiring direct contact spread more slowly.
Do masks stop viruses from spreading?
Masks reduce the number of virus-containing droplets and aerosols released into the air and can also protect the wearer from inhaling them. Their effectiveness depends on the type of mask, how well it fits, and consistent use in high-risk settings. They are one layer among hand hygiene, ventilation and vaccination.

Part of the guide: How Your Body Works →