Are swollen lips always due to an allergic reaction?

No, not always.: There are many different types of allergic reactions. Most of us think of immediate reactions to substances like foods. However, that is only one type of reaction. Some people get swollen lips from contact allergies to cosmetics, lip balms, etc. Still others develop swollen lips as part of a condition called angioedema. This condition may be caused by thyroid or autoimmune diseases or even a virus.

No: Swollen lips are not always secondary to an allergic reaction. This can occur after exposure to food allergy or another allergic trigger but it can also occur secondary to increased histamine release with no known cause. Other causes include underlying autoimmunity and inflammation. There are hereditary causes that also lead to swelling where a patient may not have associated itch.