The axilla (: axillae or axillas; also known as the armpit, underarm or oxter) is the area on the

human body The human body is the entire 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 (biology), organs and then Organ system, org ...

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 between the arm and the thoracic cage, bounded superiorly by the imaginary plane between the superior borders of the first rib,

clavicle The clavicle, collarbone, or keybone is a slender, S-shaped long bone approximately long that serves as a strut between the scapula, shoulder blade and the sternum (breastbone). There are two clavicles, one on each side of the body. The clavic ...

and

scapula The scapula (: 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 either side ...

(above which are considered part of the

neck The neck is the part of the body in many vertebrates that connects the head to the torso. It supports the weight of the head and protects the nerves that transmit sensory and motor information between the brain and the rest of the body. Addition ...

), medially by the serratus anterior muscle and

thoracolumbar fascia The thoracolumbar fascia (lumbodorsal fascia or thoracodorsal fascia) is a complex, multilayer arrangement of fascial and aponeurotic layers forming a separation between the paraspinal muscles on one side, and the muscles of the posterior abdomina ...

, 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 Glenohumeral joint, shoulder-joint. Structure The subscapularis is covere ...

, 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 dorsi'') comes from ...

. 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 ...

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 factors, ...

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

.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 dorsi'') 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. Some sources also include the pectoralis minor. It can elongate after weight loss. The contents of the axilla include the axillary vein and

artery An artery () is a blood vessel in humans and most other animals that takes oxygenated blood away from the heart in the systemic circulation to one or more parts of the body. Exceptions that carry deoxygenated blood are the pulmonary arteries in ...

, as well as the

brachial plexus The brachial plexus is a network of nerves (nerve plexus) formed by the anterior rami of the lower four Spinal nerve#Cervical nerves, cervical nerves and first Spinal nerve#Thoracic nerves, thoracic nerve (cervical spinal nerve 5, C5, Cervical spi ...

lymph nodes A lymph node, or lymph gland, is a kidney-shaped Organ (anatomy), 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 lymphoc ...

and fat. The axilla is the space between the side of the

thorax The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of mammals and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main di ...

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 is c ...

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

* Long

thoracic The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of mammals and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main ...

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 includ ...

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 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 or armpit hair, is the hair in the underarm area (''axilla''). Development Underarm or axillary hair goes through four stages of development, as staged by the Wolfsdorf Axillary Hair Scale, driven by ...

usually grows in the underarms of both

female An organism's sex is female ( symbol: ♀) if it produces the ovum (egg cell), the type of gamete (sex cell) that fuses with the male gamete (sperm cell) during sexual reproduction. A female has larger gametes than a male. Females and ...

s and

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

s, beginning in

adolescence Adolescence () is a transitional stage of human Developmental biology, physical and psychological Human development (biology), development that generally occurs during the period from puberty to adulthood (typically corresponding to the age o ...

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

aesthetic Aesthetics (also spelled esthetics) is the branch of philosophy concerned with the nature of beauty and taste, which in a broad sense incorporates the philosophy of art.Slater, B. H.Aesthetics ''Internet Encyclopedia of Philosophy,'' , acces ...

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 most culture and scenes, women retain their underarm hair for a variety of reasons, from subversion to egalitarianism to comfort or for hygienic reason. 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 against each other. Types of friction include dry, fluid, lubricated, skin, and internal -- an incomplete list. The study of t ...

sports Sport is a physical activity or game, often competitive and organized, that maintains or improves physical ability and skills. Sport may provide enjoyment to participants and entertainment to spectators. The number of participants in ...

such as

swimming Swimming is the self-propulsion of a person through water, such as saltwater or freshwater environments, usually for recreation, sport, exercise, or survival. Swimmers achieve locomotion by coordinating limb and body movements to achieve hydrody ...

Clinical significance

Like other flexion surfaces of large joints (

groin In human anatomy, the groin, also known as the inguinal region or iliac region, is the junctional area between the torso and the thigh. The groin is at the front of the body on either side of the pubic tubercle, where the lower part of the abdom ...

popliteal fossa The popliteal fossa (also referred to as hough 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 surfaces ...

cubital fossa The cubital fossa, antecubital fossa, chelidon, inside of elbow, or, humorously, wagina, is the area on the anterior side of the upper part between the arm and forearm of a human or other hominid animals. It lies anteriorly to the elbow (antecubit ...

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

found in the axilla.

Axillary intertrigo

Excessive

perspiration Perspiration, also known as sweat, is the fluid secreted by sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and Apocrine sweat gland, apocrine glands. The eccrine sweat glands are distribu ...

without adequate air circulation can result in axillary

intertrigo Intertrigo, commonly called “skin fold dermatitis”, 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 d ...

. Intertrigo is an inflammatory

skin condition A skin condition, also known as cutaneous condition, is any medical condition that affects the integumentary system—the organ system that encloses the body and includes skin, nails, and related muscle and glands. The major function of this ...

of skin folds exposed to friction or maceration in the presence of heat and moisture.Selden, Samue
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. The condition results in rash-like symptoms,

pustule A skin condition, also known as cutaneous condition, is any medical condition that affects the integumentary system—the organ system that encloses the body and includes skin, nails, and related muscle and glands. The major function of this ...

s, 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