Hi.. Can understand your concern.. As per your complain the reddish blisters that caused on you lips due to excessive sun exposure are known as SUN BLISTERS and are caused due to Heat Injury to the skin of the lips causing inflammation and blisters or ulcer formation.. It causes redness,chapping and at times pain and burning sensation of lips.. You need not to worry as the blisters and redness will slowly be resolved as the inflammation will be gradually decreased.. Along with sulfamethoxazole trimethoprim ds combination which is an antibiotic used to treat a variety of bacterial infections and cortisone cream which is steroid based cream and reduces inflammation you should apply ice wrapped in a cotton cloth over the sores at least 3 to 4 times a day as it can do wonders in relieving pain and burning as well as reduce the sores.. Applications of Aloe Vera containing cooling gels can be relieving.. In case of pain anti inflammatory painkillers like Ibuprofen can be helpful in reducing pain and inflammation.. Apply SPF 15 containing lip balms whenever you go in sun and keep the lips covered and prevention any exposure in sun.. Keep yourself well hydrated by drinking plenty of water.. Avoid using petroleum jelly as it tend to absorb more heat... Keep the lips clean and free of dirt to avoid infections.. Do not try to rupture the blisters as that can be painful as well as there can be infection.. Hopefully the blisters will heal in next 6 to 8 days.. Hope your query is solved.. Thanks and regards..