Cephalexin is not my friend. Granted I have nearly every allergy known to mankind, but it gave me blisters inside my mouth, on the soft tissue inside my lower lip. I finally realized in the middle of Sunday night that it was getting worse and thus probably not sores related to the breathing tube. My doctor's office prescribed a different antibiotic which I think is OK - so far - at least no more blistering is appearing. Fleeting moments of air thru my nose give comfort but a nasal wash right now would be so awesome!!