Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concerns.. As per your query and presentation of symptoms of reduced mouth opening to just 20 mm and also sensitive mucosa to chillies with tobacco chewing history of twenty years is due to most common reason that is Oral Submucous Fibrosis in which there is formation of thick fibrous bands below the mucosa of cheeks and lips leading to stiffening and difficulty in mouth opening.. It is a precancerous condition [although not cancer] and should be taken care of. If not taken care it can transform into malignancy and malignancy can appear as non healing ulcers in the oral cavity.. It is commonly seen in individuals with tobacco and areca nut chewing habit.. You need to consult an Oral Physician or a Dentist and get evaluated and he can advise him to apply a steroid ointment in combination with hyluronidase containing ointment to break fibres.. Intra lesional injections of steroid and hyluronidase can be advised to be injected after every 3 to 4 days.. Anti-oxident like Lycopene is also advised.. Physiotherapy like blowing cheeks, trying to open the mouth under pressure etc can be demonstrated and advise to be done daily.. Complete cessation of habit of tobacco if you have chewing is must .. For watching that it is turning malignant or not a thorough clinical evaluation has to be done and a regular followup should be done every 3 months.. Hope this information helps.. Thanks and regards. Dr.Honey Nandwani Arora..