Why do i have a bluish-purple spot on the bottom of my tongue?

Possibly .......: It could possibly be a vein (blood vessel) that is close to the surface. Like photo enclosed. If not, then, possibly you traumatized the area and have a "blood blister". See your dentist for a complete evaluation.

See image: If the blue spot is like the one circled in white, that is a vein, the sublingual vein. There are 2, one on left & one on right of underside of tongue. If the spot u mention is different, see fp or ENT to have it checked out.

A vein or lesion: You could have a vein that has been injured and is close to the surface making it appear blue. You could also have a lesion that is abnormal and should have it checked out by your doctor or dentist. Any new spot red, white or blue should be checked out if it does not go away within 2 weeks. If it is not obvious to the doctor what the spot is, they will do a biopsy and get a lab report.

Spot on Tongue: There are many reasons you could have this and the most common reasons are that it is that the veins in the floor of your mouth are visible at that location or normal discoloring. However, you still need to point it out to your dentist at your regular 6 month check up (or make the appointment if it has been more that 6 months) to be sure it isn't anything serious.