Contact Dermatitis: This is often the most common cause of a rash in the axilla due to irritation from deodorants, antiperspirants, or other personal care products. The rash typically presents as red, itchy, and sometimes blistered skin.

Intertrigo: A type of skin inflammation caused by skin-on-skin friction, often in warm, moist areas like the axilla. It can be exacerbated by sweat, heat, and lack of air circulation.
Eczema (Atopic Dermatitis): Can manifest in the axilla, especially in individuals with a history of atopic diseases. It presents as itchy, inflamed skin that can become red and cracked.
Folliculitis: An inflammation of the hair follicles, often caused by bacterial or fungal infections. It appears as small, pus-filled bumps on the skin.
Seborrheic Dermatitis: A condition causing scaly patches, red skin, and stubborn dandruff, which can also affect the axillary area.

Lymphoma: Although rare, cutaneous T-cell lymphoma (like mycosis fungoides) can initially present with skin lesions in unusual areas, including the axilla. Early diagnosis is crucial for treatment.
Infectious Diseases (e.g., Tuberculosis, Syphilis): Certain infectious diseases can cause skin manifestations, including rashes in the axilla. These conditions require prompt diagnosis and treatment to prevent serious complications.
Allergic Contact Dermatitis to Toxins: Exposure to certain toxins or allergens (like those found in some plants) can cause severe skin reactions, including in the axillary area.

Fox-Fordyce Disease: A rare skin condition characterized by the blockage of apocrine sweat glands, leading to itchy, dome-shaped bumps in the axillary and pubic areas.
Hailey-Hailey Disease (Familial Benign Pemphigus): A rare genetic disorder causing blisters and erosions in the skin's friction areas, including the axilla.
Darier Disease: A rare genetic disorder that affects the skin and sometimes presents with signs in the axillary area, among other locations.