The following are some of the reasons for the transparent blisters under the tongue: 1. The mucus gland cysts may be caused by the distribution of many small glands and glandular ducts with secretory functions in the mucosal tissue under the tongue. 2, sublingual gland cysts are also caused by sublingual gland secretion disorder, the treatment also requires surgery to remove the cyst, if necessary, the sublingual gland to remove the same time to prevent recurrence. 3, herpes disease stomatitis can also lead to blisters under the tongue; spicy or too hard food can also lead to the formation of traumatic blisters; ulcers under the tongue erosion, may also lead to blisters under the tongue. may also lead to blistering under the tongue.