| History | Cellulitis | Allergic contact dermatitis | Erythema nodosum | Papular urticaria |
| Is or was the rash itchy? | Negative | Positive | Negative | Positive |
| Is the patient febrile? | Sometimes positive | Negative | Sometimes positive | Negative (in all but the rarest cases) |
| Woods/outdoors exposure recently? | Negative | Positive | Negative | Positive |
| Portal of entry or punctum? | Sometimes positive | Negative | Negative | Sometimes positive |