Axilla (Armpit)

The axilla (pronounced “ak-SIH-luh”) is the area located between your chest and upper arm. It’s under your shoulder joint where your arm connects to your shoulder. It’s also called an armpit or underarm. The plural of axilla is “axillas” or “axillae.”

The axillas contain many important parts of your vascular system, nervous system and lymphatic system. This includes blood vessels, nerves and lymph nodes. The axillas serve as passageways for these structures to enter and exit your upper arms. The axillas also contain hair and sweat glands.

What do your armpits do?

Besides acting as a tunnel for blood vessels and nerves to pass through, your underarms have several other functions. The axillas:

• Enable you to lean forward and extend your shoulders
• Help you bend, move and rotate your arms, elbows and hands
• Produce sweat to help cool you down and control your body temperature
• Reduce friction between your arms and trunk when you’re walking or running

What is the structure of the axilla?

The axilla anatomy looks kind of like a pyramid, but it has four sides. The borders of each of your armpits are made up of various muscles. The boundaries include four walls, an open apex and a base. The axillary space includes:

• Anterior wall: The front side (anterior) is made up of the pectoralis major and pectoralis minor muscles (your pecs).
• Posterior wall: The back side (posterior) is made up of the subscapularis, teres major and latissimus dorsi muscles.
• Lateral wall: The boundary of the outside (lateral side) includes the end of the upper arm bone, along with the biceps brachii and coracobrachialis muscles.
• Medial wall: The boundary of the inside (medial side) includes the serratus anterior and intercostal muscles.
• Apex: The top of the armpit (apex) is open. It’s made up of the inside of your first rib, back border of your shoulder blade and front border of your collar bone.
• Base: The bottom of the armpit (base) is curved. It’s made up of skin and fascia that stretches between your chest wall and arm.

What are the parts of the axilla?

Within the muscular walls of the axilla, you have blood vessels, nerves, lymph nodes and sweat glands. These structures include:

• Axillary artery: The axillary artery branches off the subclavian artery (a main branch of the aorta). It’s the main artery supplying blood to your upper arm.
• Axillary vein: The axillary vein is the main vein that drains blood into your upper arm.
• Brachial plexus: The brachial plexus supplies your upper arm with nerves.
• Axillary lymph nodes: The axillary lymph nodes filter lymph fluid that drains from the mammary gland.
• Eccrine glands: The eccrine sweat glands release a clear, odorless fluid. They help cool your skin and regulate your body temperature.
• Apocrine glands: The apocrine sweat glands release a thicker fluid that creates an odor when it’s mixed with bacteria.
• Axillary hair: The hair in your armpits helps prevent skin-to-skin contact while participating in certain activities, like running.

What are common conditions and disorders that affect the axilla?

Conditions that may affect the axilla range from minor irritations to serious diseases. They include:

• Razor burn: You can develop this common skin irritation after dry shaving, shaving with a dull blade or shaving too fast.
• Armpit yeast infection: A yeast called Candida causes this fungal skin infection.
• Axillary intertrigo: This is an inflammatory skin condition in the skin folds of your underarms. It happens when you sweat excessively because there isn’t enough air circulation.
• Hidradenitis suppurativa: This is an autoimmune condition that attacks your hair follicles. It causes painful skin growths in areas of your body with sweat glands.
• Thoracic outlet syndrome: This condition occurs when the top (apex) of the axilla compresses the blood vessels and nerves between your bones.
• Cording (axillary web syndrome): Cording happens when thick cords of scar tissue form in your armpits after axillary lymph node removal for breast cancer.

When to worry about armpit pain

Pain and swelling in your armpit can be uncomfortable, but it’s not always a cause for concern. You may simply have muscle strain or a skin infection.

But swollen lymph nodes in the axilla can sometimes be the first sign of diseases like breast cancer. That’s because breast cancer spreads through the blood vessels in your lymphatic system to the axillary lymph nodes.

If you have any painful, enlarged lumps in your underarm, it’s worth a call to your healthcare provider. Get in as soon as you can if you have other symptoms, like fever or skin discoloration. Your provider’s the best person to help figure out what’s going on.

It’s also a good idea to reach out to your provider if you develop other symptoms around your armpit, like:

• Tingling
• Tenderness
• Muscle weakness
• Tightness
• Limited movement
• Rash
• Pimples
• Abscesses that drain pus