Differential Diagnosis for Warm, Red, Itchy Rash

• Single most likely diagnosis
  • Contact Dermatitis (e.g., Irritant Contact Dermatitis from pool chemicals): This is likely due to the recent exposure to the pool and the itchy, red rash on extensor surfaces. The lack of demarcation could suggest an irritant rather than an allergic reaction.
• Other Likely diagnoses
  • Allergic Contact Dermatitis (e.g., from plants or new pool products): Although the child was in the pool, new exposures to allergens like certain plants or pool chemicals could cause an allergic reaction, presenting similarly.
  • Insect Bites or Stings: Given the time of year (June) and the outdoor activity (being in the pool), insect bites could cause itchy, red lesions, though they are typically more localized.
  • Atopic Dermatitis (Eczema) Flare: If the child has a history of atopic dermatitis, the warm weather, pool chemicals, or other environmental factors could trigger a flare, presenting as itchy, red skin.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Stevens-Johnson Syndrome (SJS) or Toxic Epidermal Necrolysis (TEN): Although rare and not directly linked to pool exposure, these conditions can be triggered by medications or infections and are medical emergencies. Early recognition is crucial.
  • Invasive Bacterial Infections (e.g., Staphylococcal Scalded Skin Syndrome): Infections like SSSS, though rare in this context, can cause widespread skin lesions and are more common in children.
• Rare diagnoses
  • Phototoxicity or Photoallergic Reaction: Certain medications or substances can cause a reaction when exposed to sunlight, leading to a rash. This would be less likely without a history of new medications but could be considered.
  • Urticaria or Autoimmune Conditions: Conditions like acute urticaria or autoimmune disorders (e.g., juvenile idiopathic arthritis) could present with skin manifestations, though they would typically have additional systemic symptoms.