The underarms have been removed from the general body discussion as they represent a unique body area medically known as an intertrigenous site. Intertrigenous sites are body areas where two skin surfaces meet. They include the armpit, beneath the female breasts, and between the upper inner thighs. In persons who are obese, other intertrigenous sites may be present beneath the chin, beneath the abdomen, behind the knees, etc. Intertrigenous sites are characterized by moisture retention, skin movement, and warmth. This environment, as mentioned previously, is perfect for the growth of fungus, yeast, and bacteria, thus the intertrigenous sites are frequent sites of dermatologic disease.
Anatomy and Physiology
The armpit is a particularly interesting intertrigenous site because it combines the aforementioned factors with hair and abundant sweat glands. The armpit contains two types of sweat glands, eccrine and apocrine. Up to this point, the discussion regarding sweat glands has referred to eccrine sweat glands that produce a clear odorless sweat designed to cool the body and prevent overheating. Apocrine sweat glands do not participate in thermoregulation, but rather produce a yellowish scented sweat. Apocrine glands are well developed in skunks and deer, but not so well developed in humans. It is the scented apocrine sweat that interacts with special perfumes to produce a unique smell. It is theorized that babies who cannot see recognize their mother from the unique scent of her apocrine sweat. Indeed, there are abundant apocrine sweat glands around the areola of the breast. Other locations of apocrine sweat glands include the groin, buttocks, and scalp. Apocrine sweat provides a perfect growth media for odor producing bacteria. Further growth of these bacteria, in combination with fungus and yeast, can result in infections seen in the armpit, our next topic of discussion.
Common Dermatologic Disease Considerations
Infection is clearly the most common dermatologic condition seen in the armpits. Infection may be due to fungus, yeast, or bacteria. The most common condition seen in the armpit is known as intertrigo. This is the growth of yeast and possibly fungus in the warm moist
environment of the armpit that has had the skin barrier damaged by overhydration with eccrine sweat. Intertrigo presents as red, inflamed skin that may itch or burn. It is typically treated with a combination of topical antiyeast/antifungals and topical corticosteroid creams. Elimination of the sweat can prevent recurrence through the use of antiperspirants, discussed in Chapter 8.
Bacterial infections of the armpit are usually due to staph or strep organisms. These are the most common pathogens found in the environment and on the body. The apocrine sweat in the armpit provides an excellent bacterial growth media. If the bacterial infection involves the skin of the armpit, it is known as impetigo. If the bacterial infection involves the skin around the exit of the hair from the skin, it is known as folliculitis. Open wounds that may be scabbed or oozing pus characterize both conditions. They are treated with oral and/or topical antibiotics. Again, elimination of the sweat is key to prevention.
Hygiene Needs
It comes as no surprise that the key hygiene need in the armpit is the elimination of eccrine and apocrine sweat. Sweating is normal part of human physiology, but excessive sweating may occur in the armpits, just like on the hands and feet, and is characterized as hyperhidrosis. Controlling the sweat prevents body odor, skin barrier damage, infection, and emotionally disturbing wetness. This is the realm of antiperspirants, but oral medications and chemodenervation through botulinum toxin A are also used. These topics are more fully explored in Chapter 8.
Skin Care Needs
The skin care needs of the armpit are mainly irritation reduction from the aluminum salts used in antiperspirants and hair removal. Unfortunately, most topical antiperspirants cause irritation in the sensitive skin of the armpit. This can result in irritant contact dermatitis, especially if the skin barrier has already been damaged from overhydration. Thus, the best way to maintain the health of the armpit is to use an effective, nonirritating antiperspirant.
The armpit skin barrier may be further irritated from hair removal techniques, especially in the female. The armpit is a challenging area to shave with a razor due to its concave nature. Using a well-designed razor and shaving cream to both soften and reduce friction are key in the armpit. Depilatories are typically too irritating for armpit hair removal. However, hair removal is an important method to control armpit odor, since the hair provides a large surface area for bacterial growth. Removal of the hair limits the amount of bacteria that can be present in the armpit.