The axilla (also, armpit, underarm or oxter) is the area on the

human body The human body is the structure of a Human, human being. It is composed of many different types of Cell (biology), cells that together create Tissue (biology), tissues and subsequently organ systems. They ensure homeostasis and the life, viabi ...

directly under the shoulder joint. It includes the axillary space, an

anatomical space {{set index article In anatomy, a spatium or anatomic space is a space (cavity or gap). Anatomic spaces are often landmarks to find other important structures. When they fill with gases (such as air) or liquids (such as blood) in pathological ways, ...

within the

shoulder girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of t ...

between the arm and the thoracic cage, bounded superiorly by the imaginary

plane Plane(s) most often refers to: * Aero- or airplane, a powered, fixed-wing aircraft * Plane (geometry), a flat, 2-dimensional surface Plane or planes may also refer to: Biology * Plane (tree) or ''Platanus'', wetland native plant * Planes (gen ...

between the superior borders of the first rib, clavicle and scapula (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 and thoracolumbar fascia, anteriorly by the pectoral muscles and posteriorly by the

subscapularis The subscapularis is a large triangular muscle which fills the subscapular fossa and inserts into the lesser tubercle of the humerus and the front of the capsule of the shoulder-joint. Structure It arises from its medial two-thirds and Som ...

, teres major and latissimus dorsi muscle. The soft skin covering the lateral axilla contains many

hair Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and f ...

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 sur ...

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 pheromones, which play a role related to mate selection, although this is a controversial topic within the scientific community. The underarms seem more important than the pubic area for emitting body odor, which may be related to human bipedalism.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 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 L ...

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 The pectoralis major () is a thick, fan-shaped or triangular convergent muscle, situated at the chest of the human body. It makes up the bulk of the chest muscles and lies under the breast. Beneath the pectoralis major is the pectoralis minor, a ...

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

* Axillary artery and its branches * Axillary vein and its tributaries * Infraclavicular part of the brachial plexus * Long thoracic and

intercostobrachial nerve The intercostobrachial nerves are cutaneous branches of the intercostal nerves. Second intercostal nerve The lateral cutaneous branch of the second intercostal nerve does not divide, like the others, into an anterior and a posterior branch; it is ...

s * 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 inclu ...

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 usually grows in the underarms of both females and males, 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 the 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 th ...

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 Feminism is a range of socio-political movements and ideologies that aim to define and establish the political, economic, personal, and social equality of the sexes. Feminism incorporates the position that society prioritizes the male po ...

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 in sports such as swimming.

Clinical significance

Like other flexion surfaces of large joints ( groin, popliteal fossa, 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