Armpits Can Be Considered Unique Areas Of The Body
March 15, 2021 at 7:23 p.m.
By Max [email protected]
In technical terminology, the axillary region of the body is the area between the superior portion of the upper limb and the thorax. It is bordered by the serratus anterior and the thoracic wall medially, a part of the humerus laterally and the pectoralis muscles anteriorly.
There are still some areas of mystery surrounding the axilla. For example, anatomists do know why humans continue to have armpit hair. There are several theories; however, and even the most esteemed armpit scientists do not have any real convincing evidence which theory is correct. There may be little science to go on, but at least one published paper concluded that one of the best ways to prevent underarm odors is to remove underarm hair. The author of the paper provided an explanation. There are two kinds of sweat glands, apocrine and eccrine. Eccrine sweat glands are all over the body, while the apocrine type are concentrated in hairy spots.
Odor
Normal bacteria hanging out on your skin combine with apocrine sweat to produce an odor – the one commonly known as B.O. Eccrine glands cover most of the surface of your body, and are responsible for that thin sheen of sweat on your brow and extremities during heat and exercise. However, your armpits are abundant in apocrine glands (also found in your groin). These glands are copious in places with more hair follicles, and the sweat they secrete tends to be thicker.
As far back as history records take us, man has been aware of a distinctively malodorous scent that may emanate from his axilla. Since the axilla is remarkable anatomically for the presence of the apocrine gland, the unique body odor of this area has been popularly ascribed to this structure. Furthermore, racial differences in body odor have been related to differences in number of apocrine glands seen in the various races. The intense acridity of body odor sometimes noted under stress situations is thought to be the result of apocrine sweating. The apocrine glands in the axilla produce secretions that provide food for the microbes living therein. As a result the apocrine gland has been thought of as a “scent gland.” Microbial constituents of the skin microbe communities play an important role due to their production of volatile organic compounds.
Because of oil and sweat secretion, the armpit provides a nice home for many different kinds of bacteria. Compared to other parts of our skin, armpits are rather densely populated. Not only that, but armpit microbiomes vary from person to person. One study showed, after sampling nine people, that there were three types of armpit bacterial communities: One was dominated by Betaproteobacteria, a second by Corynebacterium, and a third by Staphylococcus. So one person's armpit bacteria won't necessarily be the same as somebody else's.
Other Primates
Studies have been done comparing the microbial communities found on the skin of humans, chimpanzees, gorillas, rhesus macaques and baboons. Human skin microbes are unique relative to those of the other primates, in terms of their diversity and their composition.
These differences appear to reflect both ancient shifts during millions of years of primate evolution and the more recent changes due to modern hygiene. Body odor plays a central role in primate society in the context of mating, child rearing, predatory protection and territorial marking. The composition of microbes on human skin might be expected to differ significantly from that of our closest relatives for at least three reasons.
First, even closely related primates differ in the distribution and abundance of different skin glands. Second, over the last 100 years, human hygienic behavior has dramatically changed such that the skin of most humans is now exposed daily to soaps, detergents and underarm products, some of which affect skin microbes. Third, microbes might differ among primate hosts as a function of their evolutionary dissimilarity.
Hair Growth
Underarm hair doesn’t grow in until puberty – when we are technically ready to reproduce. Plus, it often gets thin and sparse after menopause. One of the first signs of puberty is hair developing in the underarms and groin. The apocrine glands and this hair are under hormonal control. Hormones also make that pit hair coarse and dark.
Lymph Nodes
In addition to hair and glands the small hollow of each armpit contains a surprisingly large number of lymph nodes, approximately 20, in two clumps, though you can't usually feel them unless they're swollen. (One clump is closer to the surface than the other.) These lymph nodes are actually an important part of your body's immune system and serve to filter toxins out of tissues. They also produce a variety of immune cells known as lymphocytes that fight infection. In some kinds of breast cancer, these affected lymph nodes may have to be surgically removed.
Final Thoughts
Writing this column gave me a lesson in humility and I found the axilla to be more interesting than I ever could imagine.
Max Sherman is a medical writer and pharmacist retired from the medical device industry. His new book “Science Snippets” is available from Amazon and other book sellers. It contains a number of previously published columns. He can be reached by email at [email protected]
In technical terminology, the axillary region of the body is the area between the superior portion of the upper limb and the thorax. It is bordered by the serratus anterior and the thoracic wall medially, a part of the humerus laterally and the pectoralis muscles anteriorly.
There are still some areas of mystery surrounding the axilla. For example, anatomists do know why humans continue to have armpit hair. There are several theories; however, and even the most esteemed armpit scientists do not have any real convincing evidence which theory is correct. There may be little science to go on, but at least one published paper concluded that one of the best ways to prevent underarm odors is to remove underarm hair. The author of the paper provided an explanation. There are two kinds of sweat glands, apocrine and eccrine. Eccrine sweat glands are all over the body, while the apocrine type are concentrated in hairy spots.
Odor
Normal bacteria hanging out on your skin combine with apocrine sweat to produce an odor – the one commonly known as B.O. Eccrine glands cover most of the surface of your body, and are responsible for that thin sheen of sweat on your brow and extremities during heat and exercise. However, your armpits are abundant in apocrine glands (also found in your groin). These glands are copious in places with more hair follicles, and the sweat they secrete tends to be thicker.
As far back as history records take us, man has been aware of a distinctively malodorous scent that may emanate from his axilla. Since the axilla is remarkable anatomically for the presence of the apocrine gland, the unique body odor of this area has been popularly ascribed to this structure. Furthermore, racial differences in body odor have been related to differences in number of apocrine glands seen in the various races. The intense acridity of body odor sometimes noted under stress situations is thought to be the result of apocrine sweating. The apocrine glands in the axilla produce secretions that provide food for the microbes living therein. As a result the apocrine gland has been thought of as a “scent gland.” Microbial constituents of the skin microbe communities play an important role due to their production of volatile organic compounds.
Because of oil and sweat secretion, the armpit provides a nice home for many different kinds of bacteria. Compared to other parts of our skin, armpits are rather densely populated. Not only that, but armpit microbiomes vary from person to person. One study showed, after sampling nine people, that there were three types of armpit bacterial communities: One was dominated by Betaproteobacteria, a second by Corynebacterium, and a third by Staphylococcus. So one person's armpit bacteria won't necessarily be the same as somebody else's.
Other Primates
Studies have been done comparing the microbial communities found on the skin of humans, chimpanzees, gorillas, rhesus macaques and baboons. Human skin microbes are unique relative to those of the other primates, in terms of their diversity and their composition.
These differences appear to reflect both ancient shifts during millions of years of primate evolution and the more recent changes due to modern hygiene. Body odor plays a central role in primate society in the context of mating, child rearing, predatory protection and territorial marking. The composition of microbes on human skin might be expected to differ significantly from that of our closest relatives for at least three reasons.
First, even closely related primates differ in the distribution and abundance of different skin glands. Second, over the last 100 years, human hygienic behavior has dramatically changed such that the skin of most humans is now exposed daily to soaps, detergents and underarm products, some of which affect skin microbes. Third, microbes might differ among primate hosts as a function of their evolutionary dissimilarity.
Hair Growth
Underarm hair doesn’t grow in until puberty – when we are technically ready to reproduce. Plus, it often gets thin and sparse after menopause. One of the first signs of puberty is hair developing in the underarms and groin. The apocrine glands and this hair are under hormonal control. Hormones also make that pit hair coarse and dark.
Lymph Nodes
In addition to hair and glands the small hollow of each armpit contains a surprisingly large number of lymph nodes, approximately 20, in two clumps, though you can't usually feel them unless they're swollen. (One clump is closer to the surface than the other.) These lymph nodes are actually an important part of your body's immune system and serve to filter toxins out of tissues. They also produce a variety of immune cells known as lymphocytes that fight infection. In some kinds of breast cancer, these affected lymph nodes may have to be surgically removed.
Final Thoughts
Writing this column gave me a lesson in humility and I found the axilla to be more interesting than I ever could imagine.
Max Sherman is a medical writer and pharmacist retired from the medical device industry. His new book “Science Snippets” is available from Amazon and other book sellers. It contains a number of previously published columns. He can be reached by email at [email protected]
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