<s>[INST] My 10 year old son just developed a rash over night just in the armpit area and the tops of the thighs. we haven t changed anything and he didn t eat anything new. its flat and hot to the touch. not really spots but big blotches. any ideas? I m just not sure if i should take him in, he says it only itches alittle [/INST] Hi... Thank you for consulting in Chat Doctor. By what you quote it should be an urticaria or a simple skin allergy. You can use HY Chat Doctor.  Most important thing to be remembered is that it has a propensity to recur (called as second crop) within 10-14 days. If this happens, you can start using the same medicine, but I suggest you get the kid evaluated with your pediatrician. Hope my answer was helpful for you.  I am happy to help any time. Further clarifications and consultations on Chat Doctor are welcome. If you do not have any clarifications, you can close the discussion and rate the answer. Wish your kid good health. </s>