Brief answer:TEETHING. Hi.. Can understand your concern.. As per your complain about your son it seems it may be teething induced inflammation of gums.. This is the time when the milk teeth of infants starts erupting and many of the infants find it a bit painful as they suffer from redness,swelling and bleeding from gums.. At times the kids may have itching or soreness of gums too.. Some kids may also have saliva drooling from mouth,irritability,and difficulty sleeping.. Due to itchy and sore feelings of gums the infants have the craving to take whatever comes into their hand to mouth.Due to which they may carry some infection along with contaminated things or their fingers into mouth.. This could have been a reason for formation of blisters over his inner part of upper lips.. I would suggest you to see a dentist soon and get his check up done to confirm that whether it is due to teething or some other problem.. If it is teething you can give cold packs to his gums to relieve pain and discomfort.. Give him a refrigerated teether to bite. Feed him with cool milk.. If there is pain in gums anaesthetic gel application can help him by giving numbing effect.. If still pain is there pain killer medicine can be given only after consultation with a Paediatrician.. Hope your son gets well soon.. Thanks and regards.. Dr.Honey Nandwani Arora..