Contact Dermatitis: This is often the most common cause of labial swelling and itching, resulting from an allergic reaction or irritation to substances like cosmetics, food, or metals (e.g., nickel in jewelry). The reaction can cause redness, swelling, and intense itching.

Allergic Reactions: Allergic reactions to food, medications, or other substances can cause labial swelling and itching. Common culprits include nuts, shellfish, and certain medications.
Insect Bites or Stings: Bites or stings from insects can lead to localized swelling and itching, including on the lips.
Eczema (Atopic Dermatitis): Eczema can affect any part of the body, including the lips, leading to dryness, swelling, and itching.
Angular Cheilitis: This condition, often caused by fungal infections, can lead to inflammation and itching at the corners of the mouth, which may extend to the lips.

Angioedema: A severe, potentially life-threatening condition that can cause rapid swelling of the lips, face, and sometimes the airways. It often requires immediate medical attention.
Anaphylaxis: A severe, whole-body allergic reaction that can include symptoms like labial swelling, itching, and can progress to life-threatening complications if not promptly treated.

Sarcoidosis: A condition that can cause inflammation in various parts of the body, including the skin, and may lead to swelling and itching on the lips.
Melkersson-Rosenthal Syndrome: A rare neurological disorder characterized by recurrent, often unilateral, facial paralysis or weakness, swelling of the face and lips (usually the upper lip), and the development of folds and furrows in the tongue (fissured tongue).
Granulomatous Cheilitis: A rare condition that can cause swelling, typically of the upper lip, due to granulomatous inflammation. It may be associated with other conditions like Melkersson-Rosenthal Syndrome or orofacial granulomatosis.