Rashes of the Armpit

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The armpit is known more formally as the axilla (plural axillae).  It is a site of the body which is prone to certain types of rashes due to certain characteristics of the skin.  The skin here tends to be thinner than other locations such as the back, and it folds upon itself.  As such, it may be prone to moisture.  It is also a hair-bearing area.  Here, we provide an overview of various rashes which can affect the armpit.

Allergic Contact Dermatitis

Allergic contact dermatitis is a reaction to an external agent with which the skin comes into contact.  This is a delayed-type hypersensitivity reaction meaning that the reaction does not happen immediately but rather takes days to develop.  Applied agents could include ingredients found in deodorants, antiperspirants or shaving creams.  Sensitization is the process in which the body’s immune system recognizes the external agent as being foreign.  This can take weeks.  Upon re-exposure to the offending agent, the rash can occur in a much shorter period of time.  The rash will often follow the area where the agent was applied, often creating “unnatural” shapes and geometric borders hinting at an “outside job.”  The rash is often red, raised, and may include blisters or crusting.

Irritant Contact Dermatitis

Irritant contact dermatitis is also a reaction to an external agent with which the skin comes into contact.

  As opposed to allergic contact dermatitis, irritant contact dermatitis is not an allergic reaction.  Rather, it is an effect of a direct irritant or toxic effect of the agent on the skin.  Irritant contact dermatitis can also be the result of applied products such as deodorants, antiperspirants, soaps, or washes.

  The rash may be red, rough or scaly.  If severe, blistering may be present.


Intertrigo is a rash that occurs in the moist areas of skin folds.  Besides the armpits, it can also occur under the breasts, in groin folds, and in the folds of the abdomen.  The rash is also often accompanied by yeast, fungus or bacteria which thrive in the damp environment.  Prevention is aimed at keeping the folds dry.  When active, treatments against the inflammation as well as the presence of organisms are often recommended.


Erythrasma is a rash that occurs after infection with the Corynebacterium minutissimum bacteria.  In addition to the armpits, the rash can affect other areas with skin folds such as the groin folds, underneath the breasts, and in toe web spaces.  The rash appears reddish and/or tan and there may be slight wrinkling of the skin.  It is known for its coral-red fluorescence when illuminated with a Wood’s lamp.  This rash is most commonly treated with erythromycin

Tinea corporis

Tinea corporis is often referred to as “ringworm” although it is caused by fungus as opposed to a worm.  Depending on the location of the fungal infection, the name changes.  There are various species of fungus that cause this infection of the topmost layer of skin.  The rash may appear red and there may be accentuation of the borders.  Borders may also be slightly raised and there may be a thin layer of scale near the border of the rash.  This infection is most commonly treated with topical antifungal medications, several of which are available over the counter.

Acanthosis nigricans

Acanthosis nigricans appears as dark “velvety” plaques of the skin folds such as the armpits, groin, and around the neck.  It may be found in association with obesity, diabetes or insulin resistance, hormonal changes, certain medications or cancer.  While this condition is usually not directly treated, correction of the underlying disorder may help improve the appearance of the areas.

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