Differential Diagnosis for Recurring Rash

Single most likely diagnosis

• Heat rash or prickly heat: This condition is characterized by a recurring rash that can appear daily, especially in warm environments, causing burning and redness. The fact that it lasts for 3 hours and appears on the face and chest, but not the neck, could be consistent with heat rash, which often occurs in areas where clothing fits tightly or where the skin folds, but the absence on the neck might simply be due to less heat retention or friction in that area.

Other Likely diagnoses

• Contact dermatitis: This could be a possibility if the patient is exposed to an allergen or irritant daily, causing a reaction that appears as a burning, red rash. The pattern of occurrence (daily, same time) suggests an environmental or exposure-related cause.
• Phototoxicity or photoallergic reaction: If the patient is exposed to sunlight or certain light sources at the same time daily, and is using a new medication or product that makes them sensitive to light, this could cause a recurring rash.
• Urticaria (hives): While hives can appear anywhere on the body, the daily recurrence at a specific time could suggest an allergic reaction to something the patient is exposed to daily, such as a food, medication, or environmental allergen.

Do Not Miss (ddxs that may not be likely, but would be deadly if missed)

• Angioedema: A severe, potentially life-threatening condition that can cause swelling, redness, and burning, often in response to an allergen. It's crucial to distinguish it from other causes of rash due to its potential to compromise airways.
• Stevens-Johnson Syndrome (SJS) or Toxic Epidermal Necrolysis (TEN): These are severe skin conditions usually triggered by medications or infections. They can present with a rash, but the involvement of mucous membranes and the potential for widespread skin detachment make them medical emergencies.

Rare diagnoses

• Brachioradial pruritus: A rare condition characterized by intense itching and burning on the arms, but it could potentially affect other areas like the face and chest if the pattern of nerve involvement is atypical.
• Erythromelalgia: A disorder that causes burning pain, heat, and redness in the hands and feet, but in rare cases, it might affect other areas, including the face and chest, especially if it's the primary form related to other systemic conditions.