Cleveland Clinic logo
Search

What is the immune system?

Your immune system is a large network of organs, white blood cells, proteins and chemicals. These parts all work together to protect you from germs and other invaders. Your immune system also helps your body heal from infections and injuries.

Function

What does the immune system do

Your immune system works hard to keep you healthy. It does this by:

  • Keeping invaders (like germs) out of your body.
  • Destroying invaders.
  • Limiting how much harm the invaders can do if they’re inside your body.
  • Healing damage to your body.
  • Adapting to new challenges and threats.

Invaders your immune system protects you against include:

How does the immune system work?

When your immune system is working properly, it:

  • Tells the difference between cells that are yours and those that don’t belong in your body.
  • Activates and mobilizes to kill germs that may harm you.
  • Ends an attack once the threat is gone.
  • Learns about germs after you’ve had contact with them and develops antibodies against them.
  • Sends out antibodies to destroy germs that try to enter your body in the future.

But things don’t always go this smoothly. Sometimes, your immune system doesn’t work properly. For example, it may be too weak to fight off invaders, or it may launch too strong of a response.

Weak immune system

Many different conditions can weaken your immune system and make you more susceptible to infection. Conditions at birth are less common than those that develop later in life, like Type 2 diabetes and cancer.

Overactive immune system

At the other end of the spectrum, your immune system may react too strongly to invaders (real or perceived). It may mount an attack when there’s no invader. Or it may keep attacking after getting rid of an invader. An overactive immune system can lead to problems like autoimmune diseases or allergic reactions.


Intro Panel

We’ll help you choose the right place for your symptoms — from virtual visits and primary care to Express Care or the ER.

At the other end of the spectrum, your immune system may react too strongly to invaders (real or perceived). It may mount an attack when there’s no invader. Or it may keep attacking after getting rid of an invader. An overactive immune system can lead to problems like autoimmune diseases or allergic reactions.

Test

Our Providers

Search by name, specialty, location and more.

map

Locations & Directions

Find any of our 300+ locations.

Appointments

Appointments

Get the in person or virtual care you need.

Cleveland Clinic icon
Health Essentials logo
Subscription icon

Delivered every Tuesday!

Better health starts here

Sign up for our Health Essentials emails for expert guidance on nutrition, fitness, sleep, skin care and more

Woman with a shaved head due to chemotherapy treatment is hopeful following remission.

Survivorship

Learning you have cancer can be stressful and shocking. From the moment you get the news, you’re a survivor. As you face the challenges that go along with cancer treatment and recovery — physical and emotional — we’ll be right there with you. At Cleveland Clinic, survivorship care is one part of your journey. We offer a wide range of services, resources, clinics and support groups to help with any physical, emotional, financial and spiritual needs you might have related to your cancer diagnosis. Lending a helping hand along the way, we want you to not only survive, but thrive on this journey and beyond.

Media Panel

One

Locations

Our healthcare providers see patients at convenient locations in Ohio, Florida, Nevada and London.

Patient Stories

View all stories
New Image Here

Test New Patient Story Heena

“I remember that I once feared so greatly these days that I'm living in now. But it's not nearly as frightening when you have people walking alongside you and a good medical home with all the doctors in one place — and they talk to each other. That's tremendous.”
Read this patient story
One

Think You Have Cyclospora?

If you have symptoms of cyclospora, start with an Express Care Virtual Visit. You can also contact your primary care provider or go to one of our Express Cares or Urgent Cares. Learn when emergency care is appropriate.

Heena Test

What is cancer survivorship?

Having cancer may feel like running a hard race toward a finish line. People with cancer may keep the line in mind as they do their best to power through cancer’s challenges. Finishing treatment, however, may not always mean they’ve crossed it.

Some people are cancer-free after their initial treatment but don’t feel free from cancer. Other people still see the finish line, but they keep running into cancer. For others, the finish line they reach is very different from the one they expected.

That’s where cancer survivorship comes in. Cancer survivorship programs carry people through cancer, helping them to live as long as they can and with the best possible quality of life.

Person holding tablet looking at Cleveland Clinic doctor profiles

Physician Ratings at Cleveland Clinic

Choosing the right doctor can be difficult. How do you know that you can believe the ratings you see online? Cleveland Clinic is committed to helping you find the right physician for you with ratings you can trust.