Suggest Remedies For Light Patch Caused By Reaction To Medication On A Baby

Hi my 6 month old has light patches on his face he recently had a rash which is was told by my gp was something had proberly irritated his skin so he had a allergy to somthin he was percribed fucidin and now that has gone he has been left with these on his face what is this and how can i treat it many thanks