Differential Diagnosis for Allergic Rash on the Right Breast

• Single most likely diagnosis
  • Contact dermatitis: This is the most likely diagnosis due to the localized nature of the rash on the right breast, which could be caused by an allergic reaction to a specific substance such as laundry detergent, soap, or a new cosmetic product.
• Other Likely diagnoses
  • Atopic dermatitis (eczema): This condition can cause itchy, inflamed skin and is common in individuals with a history of allergies or asthma. The rash could be localized to the breast area due to various factors, including irritation from clothing.
  • Irritant dermatitis: Similar to contact dermatitis but caused by substances that irritate the skin rather than an allergic reaction, such as harsh soaps or friction from tight clothing.
  • Allergic reaction to a medication: If the patient has recently started a new medication, an allergic reaction could manifest as a rash, potentially localized to one area like the breast.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Inflammatory breast cancer: Although rare and less likely than other causes, inflammatory breast cancer can present with skin changes that resemble an allergic rash, including redness and swelling. It's crucial to consider this diagnosis due to its aggressive nature and poor prognosis if not treated promptly.
  • Cellulitis: A bacterial infection of the skin that can cause redness, swelling, and warmth, which might be mistaken for an allergic reaction. It requires antibiotic treatment and can lead to serious complications if not addressed.
• Rare diagnoses
  • Autoimmune disorders (e.g., pemphigus, pemphigoid): These conditions are characterized by blistering skin lesions and can sometimes present with rash-like symptoms. They are rare but important to consider due to their potential for significant morbidity.
  • Granulomatous lobular mastitis: A rare inflammatory condition of the breast that can cause skin changes, including a rash, and is often mistaken for other conditions, including cancer.