Hello. Thank you for writing to us at healthcaremagic I would keep a possibility of Fixed Drug Eruption (FDE). In Fixed drug eruption (FDE), as the name indicates, the eruption is fixed in its location. FDE or Fixed Drug Eruption is clinically characterized by dark/bluish patches that appears in response to a drug. The patches are fixed in location i.e each time a person takes the culprit drug these patches would appear at the same place. They leave behind post-inflammatory hyperpigmentation which can take months to fade. A lot of drugs can cause this kind of eruption e.g commonly implicated ones are pain killers/antipyretics, antibiotics etc which are commonly prescribed for cold, flu, diarrhea/dysentry etc cause most cases of FDE. Intake of the incriminating drug(s) causes FDE to reappear or become prominent. Therefore carefully checking the history for all the possible drugs might incriminate a particular drug which should be avoided. Regards