Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concern. As per your complain a red spot under the tongue can be due to simple reasons like a small hematoma formed due to injury with some hard food or any thing else, it can be a mucocele or a mucous cyst formed due to ruptured duct of the minor salivary gland.. It can be a beginning of formation of an apthous ulcer or canker sore.. The chances of it being cancerous with a history of smoking are few and will depend upon the clinical appearance and duration of presence of the lesion.. So I would suggest you to consult an Oral Physician and get evaluated and he can advise the treatment according to the cause.. In case of hematoma or a mucocele they are mostly self limiting and do not commonly need any treatment. Apthous ulcer also resolve on its own while if there is pain or discomfort application of numbing gel,warm saline gargles and taking multivitamin will resolve.. But in case of malignancy a biopsy will help in ruling out the exact cause and treatment will be planned accordingly.. Hope this information helps.. Thanks and regards. Dr.Honey Nandwani Arora..