Hi.. Can understand your concern.. As per your complain a persistent boil on lower lip can be due to either viral infection causing cold sores and is known as HERPES. It can also be due to allergic reaction to some lip product which you are using unknowingly.. It can also be due to irritation of the minor salivary glands present on the lips caused by sun exposure or lip biting habit or due to allergic reaction.. It can also be due to bacterial infection caused due to sharing of lip products with infected person.. I would suggest you to consult an oral pathologist or a dermatologist and get evaluated.. In case if it is due to viral infection oral and topical antiviral therapy lie Acyclovir can prevent frequent outbursts as antiviral therapy cannot cure the sores and can only prevent outbursts.. In case of allergy you should apply natural lip lubricants like aloevera gel, olive oil etc.. You should always apply SPF 15 containing lip balms before going out and if possible keep the lips covered.. Do not share your lip products with any one else.. Applying steroid based ointments and antimicrobial creams to relieve infection.. Application of ice packs can also help.. Drink plenty of water to maintain hydration and prevent chapping of lips.. Avoid touching the lesion with the tongue.. Hope your query is solved.. If you find the answer helpful please write a positive review and click on find this answer helpful as a token of appreciation.. Thanks and regards.. Dr.Honey Nandwani Arora..