The soft skin covering the lateral axilla contains many hair and sweat glands. In humans, the formation of body odor happens mostly in the axilla.[1] 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.[2] The underarms seem more important than the pubic area for emitting body odor, which may be related to human bipedalism.[3]
Structure
Boundaries
Anatomically, the boundaries of the axilla are:
superiorly: by the outer border of first rib, superior border of scapula, and posterior border of clavicle[4]
floor/base: by the skin[4] (visible surface of axilla)
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.[8] It can descend after weight loss.[9]
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.[8] It can elongate after weight loss.[9]
Superficial muscles of the chest and front of the arm.
Axillary artery and its branches - anterior view of right upper limb and thorax.
The veins of the right axilla, viewed from in front.
The right brachial plexus (infraclavicular portion) in the axillary fossa; viewed from below and in front.
The left side of the thorax.
Axilla
Axilla
Axilla
Axilla
Axilla
Axilla
Axilla
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.[10]
In some modern Western cultures, it is common for women to remove underarm hair. Some view this practice as an aesthetic matter, while others view its removal for health-related concerns.[11] As underarm hair grows quickly, removal must be performed frequently, or stubble will appear in the axilla.
In the feminist movement, the hippie culture, and in the punk rock scene, some women retain their underarm hair for a variety of reasons, from subversion to egalitarianism to comfort.[12] Conversely but uncommonly, some men choose to remove their underarm hair for aesthetic reasons or to reduce friction in sports such as swimming.
Shaved underarm
Natural underarm
Clinical significance
Like other flexion surfaces of large joints (groin, popliteal fossa, cubital fossa and essentially the anterior part of the neck), it is an area where blood vessels and nerves pass relatively superficially, and with an increased amount of lymph nodes.
Lymphogenic spread of breast cancer
Breast cancer typically spreads via lymphatic vessels to the lymph nodes found in the axilla.[13]
Axillary intertrigo
Excessive perspiration without adequate air circulation can result in axillary intertrigo. Intertrigo is an inflammatory skin condition of skin folds exposed to friction or maceration in the presence of heat and moisture.[14] 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, pustules, or chronic itching or burning in the underarm.[14] Intertrigo (in any site) has no racial or sexual predilection.[14] Axillary intertrigo is common among those who work in hot environments where air circulation is restricted by necessary clothing or safety equipment.[15]
^Turkington, Carol; Dover, Jeffrey S. (2007). The encyclopedia of skin and skin disorders (3rd ed.). New York: Facts on File. p. 363. ISBN978-0-8160-6403-8.
^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
