Your thymus is a small gland in the lymphatic system that makes and trains special white blood cells called T-cells. The T-cells help your immune system fight disease and infection. Your thymus gland produces most of your T-cells before birth. The rest are made in childhood and you’ll have all the T-cells you need for life by the time you hit puberty.


What is the thymus?

The thymus is a small gland that’s part of your lymphatic system. Your lymphatic system is made up of a network of tissues, vessels and organs such as your tonsils, spleen and appendix. Your lymphatic system is a part of your immune system. It helps defend against infection and disease.


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What does the thymus do?

The primary function of the thymus gland is to train special white blood cells called T-lymphocytes or T-cells. White blood cells (lymphocytes) travel from your bone marrow to your thymus. The lymphocytes mature and become specialized T-cells in your thymus.

After the T-cells have matured, they enter your bloodstream. They travel to your lymph nodes (groups of cells) and other organs in your lymphatic system, where they help your immune system fight disease and infection.

Your thymus gland is also part of your endocrine system. Your endocrine system makes and releases hormones that control the functions of your body. Your thymus produces and releases several hormones including:

  • Thymopoietin: fuels the production of T-cells and tells the pituitary gland to release hormones.
  • Thymosin and thymulin: help make specialized types of T-cells.
  • Thymic humoral factor: keeps your immune system working properly.

During what age is the thymus gland most active?

The thymus gland is most active during childhood. Your thymus actually starts making T-cells before you’re born. It keeps producing T-cells and you have all the T-cells you need by the time you reach puberty. After puberty, your thymus gland slowly starts to decrease in size and is replaced by fat.



Where is the thymus located?

The location of your thymus gland is in your upper chest behind your breastbone (sternum). It sits between your lungs in a part of your chest called the mediastinum. Your thymus is just in front of and above your heart.

What does the thymus gland look like?

The thymus gland is pinkish-gray. It is made up of two irregularly shaped parts (lobes). The lobes have lots of small bumps called lobules on the surface.


How big is the thymus gland?

The thymus gland is quite big in babies and children. It reaches its biggest weight of about 1 ounce during puberty. After puberty, it begins to shrink, and in older adults, it’s rather small.

Conditions and Disorders

What disorders can affect the thymus gland?

Many conditions and disorders can affect your thymus gland. The issues range from genetic disorders present at birth to diseases most commonly seen in adults. These issues include:

  • DiGeorge syndrome: A congenital (present at birth) disorder in which the thymus is missing or underdeveloped. Children born with DiGeorge syndrome have severe immunodeficiency (failure of immune system) and are at a higher risk for infections.
  • Graft-versus-host-disease: When a thymus gland is transplanted from a stillborn infant to an infant born with DiGeorge syndrome, it may help restore the infant’s immune system. However, the transplanted thymus may create cells that attack the recipient’s cells.
  • Mediastinal masses: Masses can include tumors, fluid-filled sacs (cysts) or other abnormalities in your mediastinal organs, which include the thymus. The masses may or may not be cancerous.
  • Thymoma and thymic carcinoma (thymus cancer): Thymoma and thymic carcinoma are two rare types of cancer that can form in the cells covering the outside surface of your thymus. Thymomas look like regular thymus cells, grow slowly and don’t usually spread beyond your thymus. Thymic carcinoma doesn’t look like regular thymus cells, grows faster and spread more frequently to other parts of your body. Thymoma is easier to treat than thymic carcinoma.

Some conditions can occur that are related to thymus cancer but aren’t directly caused by the thymus tumors. These conditions include:

  • Myasthenia gravis: An autoimmune disease in which your immune system forms antibodies that prevent your nerves from passing signals to your muscles, causing muscle weakness.
  • Pure red cell aplasia: A rare autoimmune disorder in which your body can’t produce new red blood cells, leading to severe anemia.
  • Hypogammaglobulinemia: A disorder in which your body produces low levels of antibodies.

Other kinds of tumors can form in your thymus as well. These tumors include lymphoma and germ cell tumors. However, these aren’t considered thymoma or thymic carcinoma.

What are the symptoms of thymus cancer?

The most common signs of thymus cancer include:

  • Thymus pain (pain in your upper chest).
  • Persistent cough.
  • Shortness of breath.
  • Hoarse voice.
  • Swelling in your face, neck, upper chest or arms.

Additional Common Questions

Can you live without a thymus?

The thymus gland is an important part of your immune system. It helps train the white blood cells that protect your immune system. Fortunately, most of your T-cells were produced before you were even born, and the rest were made during childhood and throughout puberty.

Therefore, adults don’t really need a thymus. If a baby or child has to have their thymus removed, there can be potential health issues. Removal could lead to infections, autoimmune conditions, allergies and an increased risk of cancer.

What’s the difference between the thymus and the thyroid?

Your thymus is a gland that helps protect your immune system. Your thyroid is a gland in the endocrine system. It produces hormones that control your growth and metabolism (how your body uses energy). Your thyroid is located in the front of your neck, below your voice box (larynx).

A note from Cleveland Clinic

You may not have even known it was there, but your thymus gland served an important function. As part of your lymphatic system, your thymus gland produced special white blood cells called T-cells that help your immune system. Most of your T-cells matured by the time you hit puberty, and they should help protect you against disease and infection for life. Rarely, conditions related to the thymus can occur. If you develop thymus pain or other signs of thymus cancer, talk to your healthcare provider.

Medically Reviewed

Last reviewed on 05/15/2022.

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