Hi.. Can understand your concern.. As per your complain Redness and swelling of the skin under floor of mouth along with dry mouth and altered taste can all be inter related as incomplete saliva production leading to dryness of mouth can cause thinning of oral mucosa as well as it becomes more prone to bacterial infection due to incomplete cleansing of debris and bacteria by saliva as well as atrophy of mucosa.. Altered taste can also occur due poor oral hygiene as well as due to dryness of mouth. Metallic taste can also occur due to any medication if you are taking. There are several causes which can cause all these symptoms like Diabetes, auto immune disease like Sjogren s Syndome, Certain Medicines, Damange to major salivary glands, Nerve damage,infections etc. Excessive smoking can also cause dryness of mouth and in-turn the other problems. I would suggest you to consult a doctor who will do a clinical evaluation and detailed medical history will help him giving a correct diagnosis and plan a proper treatment for you. There are certain artificial saliva agents available in the market that can help in easing your dry mouth. Certain sour candies are also available which can cause stimulation of glands thereby improving saliva production.. Drink plenty of water to improve hydration.. Gargling with plain water after meals can help in cleaning the mouth of food remnants and bacteria. Any infection in the floor of mouth can be treated by antibiotics but only after clinical evaluation. Hope your query is solved.. Thanks and regards.. Dr.Honey Nandwani Arora.