Ranula: A type of mucocele that occurs under the tongue, often caused by the obstruction of the sublingual gland or duct. It is a common and benign condition that presents as a swelling under the tongue.

Mucocele: Similar to a ranula but can occur in other parts of the mouth. It's caused by the obstruction of a salivary gland or duct, leading to the accumulation of mucin.
Sublingual gland inflammation or infection: Inflammation or infection of the sublingual gland can cause swelling under the tongue.
Trauma: Injury to the area under the tongue can lead to swelling due to hematoma or abscess formation.
Allergic reaction: An allergic reaction can cause swelling under the tongue, especially if it's part of a more generalized allergic response like angioedema.

Angioedema: A severe, potentially life-threatening condition that can cause rapid swelling of the tissues under the tongue, which can compromise the airway.
Ludwig's angina: A severe infection of the tissues in the neck, which can cause swelling under the tongue and can lead to airway obstruction if not promptly treated.
Tongue cancer: Although less common, cancer of the tongue or floor of the mouth can present as a swelling under the tongue and is critical to diagnose early.

Cystic hygroma: A rare congenital condition that can present as a swelling under the tongue due to a lymphatic malformation.
Dermoid cyst: A rare type of cyst that can occur under the tongue, often present at birth or discovered during childhood.
Sublingual thyroid: A rare condition where thyroid tissue is located under the tongue, which can cause swelling in this area.