A person’s lips can swell on one side for several reasons, such as allergic reactions, injuries, or long-term medical conditions.

Keep reading to explore why a person’s lip may swell on one side, and the treatment options available.

Injury to the mouth can cause the lips to swell on either side, depending on the damage.


According to the University of Rochester Medical Center, a person can apply an ice pack to the injury every 1–2 hours for 10–15 minutes for the first 24 hours.

A person can also suck on ice cubes or ice pops.

Angioedema refers to a reaction that causes rapid swelling of the skin and mucous membranes.

According to DermNet, it most commonly affects the eyes, lips, tongue, hands, feet, and genitals. It does not typically last long and disappears within 24–48 hours.

There are a few different types of angioedema:

  • Allergic reaction: This can be due to insect bites, certain foods, natural rubber latex, and other substances.
  • Non-allergic drug reaction: This occurs due to particular medications, such as angiotensin-converting enzyme inhibitors.
  • Idiopathic: Healthcare professionals do not know the exact cause, but it may be due to some autoimmune disorders.

Angioedema can also be hereditary, but this is rare.

Symptoms of angioedema include:

  • flushed skin
  • swelling below the skin’s surface
  • swellings that may or may not be itchy, painful, or tender

Learn more about angioedema here.


Treatment typically depends on the cause. In severe cases, a person may need to go to the hospital to ensure their airways are open, and they do not have difficulty breathing.

A person can develop swollen lips from allergic reactions to certain foods, medications, insect stings and bites, or environmental triggers such as dust or pollen. Healthcare professionals call this allergic angioedema.

The Centers for Disease Control and Prevention (CDC) estimate that 8% of children in America have some form of food allergy.

Most food-related allergy symptoms start within 2 hours after consumption, but they can begin within minutes.

Symptoms of an allergic reaction include:

  • stomach cramps
  • hives
  • shortness of breath
  • wheezing
  • coughing
  • vomiting
  • tongue and lip swelling

Oral allergy syndrome is an allergic reaction to uncooked foods, such as fruits, vegetables, nuts, and seeds. It occurs due to an allergy to pollen on the food, causing a reaction in the mouth. It may cause the lips to swell where the food has come into contact with the skin.


A severe allergic reaction can cause anaphylaxis, which is a medical emergency.

Anaphylaxis makes breathing difficult due to the swelling of the tongue and throat. It can cause a person to go into shock.

An injection of adrenaline, or epinephrine, is the first treatment for anaphylaxis. People may know this as an EpiPen.

A person should call an ambulance and administer an EpiPen as quickly as possible after anaphylaxis. If symptoms do not ease with adrenaline, people can deliver another dose 5 minutes after the first injection.


A person cannot cure their allergies. However, they can take medications to help manage them.

Learn more about the treatment options for allergies here.

Cellulitis is a bacterial infection that enters the deeper layers of the skin through a wound or abrasion.

It commonly occurs in the arms and legs, but it can also affect the skin around the eyes, mouth, anus, or stomach.

Symptoms of cellulitis include:

If a person experiences numbness, fever, or cellulitis that affects a large area, they should quickly seek medical advice.


A doctor will prescribe antibiotics to treat cellulitis.

Learn more about the treatment options for cellulitis here.

The following viral infections may cause a person’s lip to swell on one side.

Cold sores

Cold sores occur due to the herpes simplex virus.

Symptoms of a cold sore infection include a painful blister, typically on one side of the lips. A person can also experience tingling and swelling.

Once the blister forms, they can ooze fluid and then crust over.

In children, the first cold sore that develops may cause the inside of the mouth to become very swollen and painful.


Cold sores typically resolve within 1–2 weeks. Until then, a person can use antiviral gels, ointments, creams, and patches.

Learn more about the treatment options for cold sores online.

Hand, foot, and mouth disease

Hand, foot, and mouth disease (HFMD) occurs due to the coxsackie A16 virus and other types of enterovirus.

HFMD can cause ulcers and sores on the lips, which may lead to swelling.

Other symptoms include small flushed spots and water blisters on the hands and feet, particularly on the palms, soles, fingers, and toes.

Painful ulcers can also form in the mouth and on the tongue.

Learn more about hand, foot, and mouth disease here.


There is no particular treatment for HFMD. A person can take over-the-counter pain medication to help reduce fever and discomfort. Numbing mouthwashes may also ease the pain.

Dental braces can irritate the mouth’s inner lining and cause cuts or abrasions that lead to a swollen lip.

Nickel allergies may also cause lip swelling, as nickel is present in metal braces.


Braces that do not contain nickel are available, and dentists can use wax on metal braces to protect the mouth from injury.

The following are less common causes of a swollen lip.

Granulomatous cheilitis

Granulomatous cheilitis is an uncommon condition that causes the lips to become swollen.

It can occur in people of any age, race, and sex, although it typically occurs in early adulthood.

Granulomatous cheilitis can occur due to:

The first symptom is a sudden swelling of the upper lip. This can disappear within hours or days, but the swelling may return and worsen each time.


Topical corticosteroids, anti-inflammatory antibiotics, nonsteroidal anti-inflammatory medication (NSAIDs), or surgical reduction are treatment options for granulomatous cheilitis.

If an underlying allergy or disease causes the swelling, a person will need medical treatment for these conditions.

Melkersson-Rosenthal syndrome

According to the National Organization of Rare Disorders, Melkersson-Rosenthal syndrome (MRS) is a rare neurological disorder that causes long-lasting, recurrent face swelling.

MRS can also cause weakness in the facial muscles and a fissured tongue.

It is similar to granulomatous cheilitis, where the first symptom is often swelling in the upper lip, but it can also first affect the lower lip, the cheeks, eyelids, or one side of the scalp.

The swelling in MRS may become permanent and will continue to return once the first episode passes.


Although most symptoms resolve without medical care, episodes may last longer and occur more often if a person does not seek treatment.

Treatments include:

  • corticosteroid injections
  • NSAIDs
  • antibiotics
  • surgery

Embouchure collapse

Embouchure collapse is a type of focal dystonia or movement disorder.

It can affect people who play brass or woodwind instruments, as they have to maintain a specific position with their mouths for long periods.

This condition causes swelling in a person’s lips. They need to rest before they play again.

Lip cancer

Lip cancer is the most common type of mouth cancer, which usually develops in the squamous cells that line the lips and mouth. Melanoma can also develop on the lips.

Risk factors for lip cancer include:

  • using tobacco
  • consuming excessive amounts of alcohol
  • high levels of sun exposure

Symptoms of lip cancer include sores that do not heal, swelling, lumps, bleeding, pain, and numbness in the lips.


Treatments for lip cancer can include surgically removing cancerous tissue or using radiation or chemotherapy to reduce tumors and kill cancer cells.

Seeing a doctor may not always be necessary for a swollen lip.

However, if people experience more severe symptoms or signs of a serious disease, such as recurring swelling or a growth, they should see a doctor.

A person should seek advice from a doctor if bleeding from lip wounds does not stop, or if an injury is deep, covers a large area, or shows signs of infection.

If a person experiences symptoms of anaphylaxis, they should seek medical attention immediately. Anaphylactic reactions can be fatal.

People should also seek emergency medical care for severe injuries caused by an animal or human bite, injuries that puncture the mouth or lips, or if there are head injuries.

There can be many reasons for a person’s swollen lip.

Often, the swelling will resolve on its own.

However, seek medical advice where a swelling does not improve, comes back, or develops alongside severe symptoms, such as difficulty breathing.