Doc, what's this itchy rash?
Answer: Contact dermatitis from poison ivy
We see a variety of rashes in the Emergency Department. The first step is to accurately describe the rash. Is this a macule or nodule? Is this a vesicle or bulla? The next step is to quickly "profile" the rash to see if it fits any classic pattern by patient age, rash distribution, or presence of hypotension. And finally, if you are still stumped, use an algorithm based on the rash type.
These figures are from March 2010's Emergency Medicine Magazine (it's free!). It's not meant to be a comprehensive article on rashes but it sure does take the guesswork out of 90% of the rashes you see.
Thanks to Dr. Hemal Kanzaria for including this idea as a PV card.