The swelling of the veins under the tongue is most likely a condition called sublingual varices, which are dilated and tortuous veins that can be seen along the lower surface of the tongue or the floor of the mouth, and become more prominent with age, but they may be associated with two syndromes in younger people.

• Fabry syndrome: It is a rare and potentially dangerous genetic disease, which is caused by the body’s failure to produce an enzyme called alpha-galactosidase A. Its benefit is to prevent the accumulation of a fat-like substance called sphingolipids in blood vessels, and it may affect various body organs such as the brain, heart, and kidneys.
• Osler syndrome: It is also a rare genetic disorder, and it results in abnormal connections between arteries and veins, and these blood vessels may expand over time, and they may rupture, causing serious complications.

Swelling under the tongue can be noticed by the patient himself or by the dentist, and it is a benign venous problem without symptoms. There are many suggested explanations that researchers acknowledge as risk factors for this condition, according to what is mentioned in the sources, including: smoking, cardiovascular diseases such as high blood pressure, diabetes, chronic cough, wearing dentures, vitamin C deficiency, and venous insufficiency.

If you are concerned about swollen veins under the tongue, it is best to go to the doctor to get the necessary advice.