Swollen lips are caused by underlying inflammation or a build-up of fluid under the skin of your lips. Many things can cause swollen lips, from minor skin conditions to severe allergic reactions. Allergies to certain foods, medications, or the bite or sting of an insect are fairly common triggers for swollen lips and other symptoms. Foods often associated with allergies include, milk, eggs, peanuts, shellfish, soy, wheat etc..

When you encounter something you're allergic to, your body produces a chemical called histamine. The release of histamine can lead to classic allergy symptoms, such as sneezing, itchy skin, and inflammation. This inflammation may cause swollen lips.

Waking up with a swollen lip can be an alarming discovery, especially if there wasn’t an obvious mouth injury the day before. In addition to sudden trauma to the mouth, there are several common conditions that can cause swollen lips to appear in the morning. These include a variety of allergic reactions, as well as medical conditions affecting the skin, nerves, or face muscles. Dental work can also trigger inflammation that causes your lips to swell.

Depending on the cause, a swollen lip can develop over several hours. This means you can go to bed with no signs of trouble and wake up looking and feeling much different. And if the cause isn’t obvious, you may need to look for other symptoms or think back to what you were exposed to that might provide an explanation.

Allergies to certain foods, medications, or the bite or sting of an insect are fairly common triggers for swollen lips and other symptoms.