Axilla


The axilla is the area on the human body directly under the joint where the arm connects to the shoulder. It also contains many sweat glands.
In humans, the formation of body odor happens mostly in the armpit. These odorant substances have been suggested by some to serve as pheromones, which play a role related to mating. However, this is a controversial topic within the scientific community. The underarm regions seem more important than the genital region for body odor, which may be related to human bipedalism.

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
medially: serratus anterior and by the ribcageanteriorly: by the pectoralis major, minor, and subclavius
posteriorly: by the subscapularis above, and teres major and latissimus dorsi below		laterally: by the intertubercular sulcus
floor/base: by the skin

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

Contents

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.
The term oxter is used in the Scots language and in Ireland instead of "axilla".

Tickling

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

Underarm hair

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

Axillary intertrigo

Excessive perspiration can result in axillary intertrigo. Intertrigo is an inflamed skin condition caused by heat, friction, and moisture. A warm, wet underarm may accommodate the growth of pathogenic bacteria, yeasts, and fungi. The condition is responsible for rash-like symptoms, pustules, or chronic itching or burning in the underarm. Axillary intertrigo is common among those who work in hot environments.