The axilla (also, armpit, underarm or oxter) is the area on the human body directly under the shoulder joint. It includes the axillary space, an anatomical space within the shoulder girdle between the arm and the thoracic cage, bounded superiorly by the imaginary plane between the superior borders of the first rib, clavicle and

scapula The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eithe ...

(above which are considered part of the

neck The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...

), medially by the

serratus anterior muscle The serratus anterior is a muscle that originates on the surface of the 1st to 8th ribs at the side of the chest and inserts along the entire anterior length of the medial border of the scapula. The serratus anterior acts to pull the scapula fo ...

and thoracolumbar fascia, anteriorly by the pectoral muscles and posteriorly by the subscapularis, teres major and

latissimus dorsi muscle The latissimus dorsi () is a large, flat muscle on the back that stretches to the sides, behind the arm, and is partly covered by the trapezius on the back near the midline. The word latissimus dorsi (plural: ''latissimi dorsorum'') comes from ...

. The soft skin covering the lateral axilla contains many hair and

sweat gland Sweat glands, also known as sudoriferous or sudoriparous glands, , are small tubular structures of the skin that produce sweat. Sweat glands are a type of exocrine gland, which are glands that produce and secrete substances onto an epithelial s ...

s. In humans, the formation of

body odor Body odor or body odour (BO) is present in all animals and its intensity can be influenced by many factors (behavioral patterns, survival strategies). Body odor has a strong genetic basis, but can also be strongly influenced by various diseases ...

happens mostly in the axilla. These odorant substances have been suggested by some to serve as

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

s, which play a role related to

mate selection Mate choice is one of the primary mechanisms under which evolution can occur. It is characterized by a "selective response by animals to particular stimuli" which can be observed as behavior.Bateson, Paul Patrick Gordon. "Mate Choice." Mate Choic ...

, although this is a controversial topic within the scientific community. The underarms seem more important than the

pubic area Pubic hair is terminal body hair that is found in the genital area of adolescent and adult humans. The hair is located on and around the sex organs and sometimes at the top of the inside of the thighs. In the pubic region around the pubis bo ...

for emitting body odor, which may be related to human

bipedalism Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' ...

.The Oxford Handbook of Evolutionary Psychology, Edited by Robin Dunbar and Louise Barret, Oxford University Press, 2007, Chapter 22 Body odours and body odour preferences in humans by Claus Wedekind

Structure

Boundaries

Anatomically, the boundaries of the ''axilla'' are: The lower posterior boundary is called the posterior axillary fold and this is a compound structure consisting of the latissimus dorsi and teres major muscles. It can descend after weight loss. The anterior boundary is called the anterior axillary fold and this is rounded in shape and formed by the lower border of the pectoralis major. Some sources also include the pectoralis minor. It can elongate after weight loss. The contents of the axilla include the axillary vein and artery, as well as the

brachial plexus The brachial plexus is a network () of nerves formed by the anterior rami of the lower four cervical nerves and first thoracic nerve ( C5, C6, C7, C8, and T1). This plexus extends from the spinal cord, through the cervicoaxillary canal in th ...

lymph nodes A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that incl ...

and fat. The axilla is the space between the side of the thorax and the upper arm.

Axillary artery In human anatomy, the axillary artery is a large blood vessel that conveys oxygenated blood to the lateral aspect of the thorax, the axilla (armpit) and the upper limb. Its origin is at the lateral margin of the first rib, before which it i ...

and its branches * Axillary vein and its tributaries * Infraclavicular part of the

* Long thoracic and intercostobrachial nerves * Five groups of axillary

lymph node A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that inc ...

s and the associated lymphatics * Axillary fat and areolar tissue in which the other contents are embedded

Society and culture

The term "underarm" typically refers to the outer surface of the axilla. However, the terms are sometimes used interchangeably in casual contexts. Colloquially, ''underarm '' refers to the hollow beneath the junction of the arm and shoulder.

Tickling

The underarm is a ticklish area, possibly due to the number of nerves it contains. Most people find this area to be particularly unpleasant when tickled.

Underarm hair

Underarm hair Underarm hair, also known as axillary hair, is the hair in the underarm area (''axilla''). Development Underarm or axillary hair goes through four stages of development, driven by weak androgens produced by the adrenal in males and females ...

usually grows in the underarms of both

female Female (symbol: ♀) is the sex of an organism that produces the large non-motile ova (egg cells), the type of gamete (sex cell) that fuses with the male gamete during sexual reproduction. A female has larger gametes than a male. Females a ...

s and

male Male (Mars symbol, symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization. A male organism cannot sexual reproduction, repro ...

s, beginning in

adolescence Adolescence () is a transitional stage of physical and psychological development that generally occurs during the period from puberty to adulthood (typically corresponding to the age of majority). Adolescence is usually associated with t ...

. In some modern Western cultures, it is common for women to remove underarm hair. Some view this practice as an

aesthetic Aesthetics, or esthetics, is a branch of philosophy that deals with the nature of beauty and taste, as well as the philosophy of art (its own area of philosophy that comes out of aesthetics). It examines aesthetic values, often expressed t ...

matter, while others view its removal for health-related concerns. As underarm hair grows quickly, removal must be performed frequently, or stubble will appear in the axilla. In the Islamic tradition, underarm hair removal is a religious hygiene practice for both women and men. While most Muslims shave it, some pluck it, with products like wax, as it's more efficient to sustain longer periods without regrowing. In the feminist movement, the

hippie A hippie, also spelled hippy, especially in British English, is someone associated with the counterculture of the 1960s, originally a youth movement that began in the United States during the mid-1960s and spread to different countries around ...

culture, and in the punk rock scene, some women retain their underarm hair for a variety of reasons, from subversion to egalitarianism to comfort. Conversely but uncommonly, some men choose to remove their underarm hair for aesthetic reasons or to reduce

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding (motion), sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative la ...

sports Sport pertains to any form of competitive physical activity or game that aims to use, maintain, or improve physical ability and skills while providing enjoyment to participants and, in some cases, entertainment to spectators. Sports can, ...

such as swimming.

Clinical significance

Like other flexion surfaces of large joints (

groin In human anatomy, the groin (the adjective is ''inguinal'', as in inguinal canal) is the junctional area (also known as the inguinal region) between the abdomen and the thigh on either side of the pubic bone. This is also known as the medial co ...

popliteal fossa The popliteal fossa (also referred to as hough, ">/sup> or kneepit in analogy to the cubital fossa) is a shallow depression located at the back of the knee joint. The bones of the popliteal fossa are the femur and the tibia. Like other flexion ...

, cubital fossa and essentially the anterior part of the

), it is an area where blood vessels and nerves pass relatively superficially, and with an increased amount of

Lymphogenic spread of breast cancer

Breast cancer typically spreads via lymphatic vessels to the lymph nodes found in the axilla.

Axillary intertrigo

Excessive perspiration without adequate air circulation can result in axillary

intertrigo Intertrigo refers to a type of inflammatory rash (dermatitis) of the superficial skin that occurs within a person's body folds. These areas are more susceptible to irritation and subsequent infection due to factors that promote skin breakdown such ...

. Intertrigo is an inflammatory skin condition of skin folds exposed to friction or maceration in the presence of heat and moisture.Selden, Samuel, MD
Intertrigo
emedicine, WebMD. March 9, 2007. Accessed May 21, 2009. Intertrigo is worsened by infection, usually fungal ( Candida yeast species), but also bacterial or viral; warm, wet underarms promote those growths.Occupational Dermatoses - A Program for Physicians
National Institute for Occupational Safety and Health. April 17, 2001. Accessed May 21, 2009. The condition results in rash-like symptoms, pustules, or chronic itching or burning in the underarm. Intertrigo (in any site) has no racial or sexual predilection. Axillary intertrigo is common among those who work in hot environments where air circulation is restricted by necessary clothing or safety equipment.

Notes

External links

Step by step Video dissection of the Human Axilla showing all relevant anatomy
* * {{Authority control Upper limb anatomy