<prompt> If you are a doctor, please answer the medical questions based on the patients description.my 20 month old has a red rash from her ankles to, and including her butt, almost looks like bad sun burn, but is raised like a welt. It is starting to spread to her hips and small areas on her upper arm. She hasn t eaten anything abnormal and we haven t changed detergents.  <response>: Hello, This might be Urticaria hypersensitivity reaction? Maybe contact Dermatitis Atomic Dermatitis! I just hope that there is No cold fever! Please just dont get panic. If the baby is fine: no crying Itching then just wait and watch. If its itching painfulexcessive crying then you need to give medication like Antihistamines. Hope I have answered your query. Let me know if I can assist you further. Take care Chat Doctor. 