Differential Diagnosis for Red Rash After Swimming

The patient's presentation of a red rash all over her body after swimming in a swimming pool can be approached by considering several potential diagnoses, categorized based on their likelihood and potential impact on the patient's health.

• Single Most Likely Diagnosis

  • Irritant Contact Dermatitis: This is a common condition that can occur after exposure to irritants such as chlorine in swimming pools. The rash is typically red, non-itchy, and appears shortly after exposure, making it a likely explanation for the patient's symptoms.

• Other Likely Diagnoses

  • Allergic Contact Dermatitis: Although less common than irritant contact dermatitis, an allergic reaction to substances in the pool or pool products (like certain disinfectants) could cause a rash. However, this is usually itchy.
  • Seawater or Pool Water Irritation: Certain components in the water, aside from chlorine, could cause irritation, especially if the pool is not well maintained.
  • Urticaria: This could be a reaction to something in the pool water or an allergic reaction, but it's typically itchy and may not cover the entire body uniformly.

• Do Not Miss Diagnoses

  • Anaphylaxis: Although rare and typically presents with more systemic symptoms (such as difficulty breathing, rapid heartbeat, and a fall in blood pressure), a severe allergic reaction to something in the pool could potentially start with a rash. It's crucial to rule out anaphylaxis due to its potentially fatal outcome if not treated promptly.
  • Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis (SJS/TEN): These are severe skin conditions usually triggered by medications or infections but could potentially be triggered by an unusual reaction to pool chemicals. They are characterized by widespread skin necrosis and detachment and are medical emergencies.

• Rare Diagnoses

  • Erythema Multiforme: A skin condition characterized by target lesions, which could be triggered by infections or medications. It's less likely to be directly related to swimming pool exposure but could be considered if other symptoms are present.
  • Phototoxic Reaction: Certain substances can cause a phototoxic reaction when exposed to sunlight, potentially exacerbated by pool chemicals. However, this would typically require exposure to sunlight after applying or being exposed to the sensitizing substance.