The Armpit (Human Anatomy): Picture, Function, Parts, Conditions, & More

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Human Anatomy

Picture of the Armpit

The arrangement of the chest wall, shoulder bones and muscles, and the upper arm create a small hollow called the armpit. The armpit is the underside of the shoulder joint, and is among the warmest areas of the body. The armpit is also called the axilla.

Blood and lymph vessels serving the arm travel through the armpit. There are more than 20 lymph nodes (small lumps of tissue that are part of the body's lymphatic system, which helps fight infection) in the armpit. These lymph nodes normally cannot be felt through the skin. The armpits have a high concentration of hair follicles and sweat glands.

Armpit Conditions

• Hyperhidrosis: Excessive sweating, which often affects the armpits and hands. The cause is unknown; the perspiration is not due to anxiety or stress.   
• Irritant contact dermatitis: Skin inflammation (redness, swelling, pain, or heat) caused by an irritating substance touching the skin. Soaps, deodorant, alcohol, and dry air may all cause irritant contact dermatitis of the armpit.
• Allergic contact dermatitis: An allergic reaction to something directly touching the skin, usually causing redness and small blisters. Irritant contact dermatitis affects the armpit more often than allergic contact dermatitis.
• Psoriasis: The armpits are often affected by psoriasis, a condition causing red plaques with a silvery scale to appear on the skin. Psoriasis is an autoimmune condition, meaning it is caused when the immune system mistakenly attacks the body's own tissues.
• Acanthosis nigricans: A skin disorder causing velvety, light brown to black markings on the skin of the armpits, neck, groin, and/or under the breasts.
• Tinea corporis (ringworm): A fungal infection of the uppermost layer of the skin (epidermis). Ringworm often creates a ring-shaped rash, although no worm is involved.
• Tinea axillaris: A term occasionally used for ringworm affecting the armpit.
• Candidiasis (yeast infection): A skin infection by the yeast Candida, causing irritated skin with white plaques. Candida grows best on warm, moist skin, and may affect the armpits.
• Intertrigo: A condition in which moist, warm skin becomes irritated and often mildly infected. Redness, itching, and burning of the skin in the armpits are common symptoms of intertrigo.
• Armpit abscess: When infected fluid (pus) collects in the armpit. The bacteria Staphylococcus is the most common cause.
• Hidradenitis suppurativa: A long-term (chronic) condition causing red, tender bumps in the skin of the armpits and/or groin. The bumps often turn into abscesses and can cause scarring over time.
• Erythrasma: A long-term (chronic) skin infection caused by the bacteria Corynebacterium. The infection causes red-brown, irritated patches of skin in the armpits or other moist areas of skin.
• Armpit boil (furuncle): A skin infection of a single hair follicle and surrounding skin. It causes a painful, red lump on the skin, which may grow into an abscess.
• Armpit folliculitis: Inflammation of the hair follicles, usually caused by bacterial infection. Most folliculitis is mild and goes away without specific treatment.
• Axillary lymphadenopathy: Enlargement of the lymph nodes of one or both armpits. The swelling may be caused by infection, cancer, or other causes and may be detected during a doctor’s examination or on imaging tests.
• Armpit skin tags (acrochordons): Harmless, small flaps of skin that commonly occur on the neck or armpits. Skin tags are more common with older age.