Hi Dear, Understanding your concern. As per your query black patch on your bottom lip could be due to many causes like post inflammatory hyper-pigmentation, excessive exposure to sun light, minor trauma or contagious like herpes, canker or allergic etc. It could be due to minor traumatization of blood vessels. Because of this which keeps on forming small spots on lips due to under skin blood accumulation. I would suggest you to consult dermatologist for proper examination of these black patches and go for biopsy. I would suggest you to maintain good oral hygiene and avoid hot and spicy foods. Take folic acid with vitamin b complex supplement. Keep drinking plenty of water. Give cold compresses twice a day which help in reducing swelling if any. Take cotton dipper in apple cedar vinegar and apply on lips. You should take antihistamines drugs to combat allergic cause. Hope your concern has been resolved. Best Wishes, Get Well Soon. Dr. Harry Maheshwari