A rash in the underarm or armpit may result from allergies, infections and autoimmune disorders such as rheumatoid arthritis, Kawasaki disease and systemic lupus erythematosus, according to Healthgrades. Certain medications, stress and exposure to excessive heat or cold may also cause underarm rashes.
Allergens that may result in underarm rashes include cosmetics, poison ivy, industrial chemicals found in latex and rubber, and insect bites, including bee stings, as noted by Healthgrades. Eczema and folliculitis constitute other allergic reactions that may also cause underarm rashes. Infections that may cause rashes include impetigo, meningitis, chickenpox, measles and ringworm. Other infectious causes of underarm rashes include strep throat, rocky mountain spotted fever and lyme disease.
An underarm rash is a symptom in which the underarm skin reddens, swells and becomes blotchy, and it may also cause tenderness, inflammation, itching, headache and sore throat, according to Healthgrades. It may result in life threatening symptoms, such as fever, difficulty breathing, sudden face inflammation and throat constriction, but the underlying cause determines the nature and severity of the symptoms. An individual should visit a doctor immediately when serious symptoms of underarm rashes appear to avoid possible complications, which include paralysis, irreversible loss of hearing, arthritis and miscarriage. Meningitis and encephalitis, which is a condition that causes swelling in the brain, are other possible complications of untreated underarm rashes.