My lip has suddenly swollen: why does it happen, and when is it 112?

The lip is made up of thin skin and mouth lining over loose connective tissue with a rich blood supply. This loose tissue readily collects fluid leaking from the blood vessels, which is why a lip can double in size within minutes or hours. The NHS defines angioedema as sudden swelling of part of the body, and lists the face, especially the lips, the tongue and the eyelids, among the areas most often affected. MSD Manuals adds that the swelling may not be equal on both sides and may be slightly painful; so one lip, or even one half of a lip, swelling fits this picture.

The first and most useful clue for telling the causes apart is whether there are hives on the skin (itchy, raised patches that are red or have pale centres). The NHS writes that swelling caused by an allergic reaction usually comes with an itchy, raised rash. MSD states that hereditary and acquired angioedema resemble the allergic kind but do not cause hives, and that ACE inhibitors can also cause angioedema without hives. This is the first check you can do at home: look at your body, arms and neck. If there are itchy raised patches, allergy is more likely; if there are none at all, a medicine or an inherited cause is more likely.

This distinction matters not only for diagnosis but also for treatment. MSD writes that with mild angioedema accompanied by hives, antihistamines partly relieve the itching and reduce the swelling, but that with angioedema without hives, for example that caused by an ACE inhibitor or an inherited cause, antihistamines, steroids and adrenaline may not work. That is why taking an allergy tablet at home and waiting for the swelling to go down is not a reliable plan for swelling without hives.

ACE inhibitors are medicines used to treat high blood pressure and heart failure, whose active ingredient names mostly end in -pril: enalapril, ramipril, lisinopril, perindopril and so on. MSD writes that the swelling caused by these medicines mostly affects the face and the upper airway. In the OCTAVE trial of 25,302 patients, angioedema occurred in 0.68% of those taking enalapril for 24 weeks. What makes this picture insidious is its timing: a case review describes swelling appearing late, with a medicine that had been taken for years without any problem, and recommends asking about the medicine with every unexplained swelling around the mouth. MSD states that if an ACE inhibitor is the cause, symptoms usually subside within 24 to 48 hours of stopping the medicine. Do not stop the medicine yourself; any change is made by the doctor who prescribed it.

What decides how dangerous lip swelling is, is whether the swelling stays in the lip. In a study at three university hospitals in the United States of 311 patients who came to A&E with angioedema caused by an ACE inhibitor, all of whom had their larynx examined with a thin camera by an ENT specialist, the need for an airway intervention was low in those with swelling of only the face, the lower lip or the upper lip. Involvement of the tongue, soft palate and larynx, however, clearly raised this risk; with swelling of the vocal cords, the odds ratio was 33.5. Difficulty swallowing, a change in the voice, drooling, shortness of breath and a feeling of a lump in the throat were associated with needing an intervention; the patients who needed one had mostly arrived within 4 hours of the symptoms starting.

This result does not make lip swelling unimportant. The NHS puts sudden swelling of the lips, mouth, throat or tongue directly on its 999 list, because at the start nobody can know whether swelling that begins in the lip will move on to the tongue and throat. The study's meaning at home is something else: if, while your lip is swollen, you notice your tongue getting thicker, your voice becoming hoarse or that you cannot swallow your saliva, that is a sign the picture has moved into its most dangerous part, and every minute counts.

Hereditary angioedema is rare, but it crosses paths directly with dentistry. MSD writes that this condition is caused by a lack or malfunction of an immune protein called C1 inhibitor, and that it does not cause hives; it states that with recurring swelling without hives, or a family history of similar swelling, doctors request tests for it. In a study from the Romanian hereditary angioedema registry, 47.6% of patients had experienced swelling suggesting this condition after dental procedures before they were diagnosed, and 86.2% of these patients had been given steroids and antihistamines before diagnosis. If your lip or face swells again and again after dental treatment, ask your doctor about this possibility.

The causes other than angioedema have their own signature. A mucocele is a painless, round blister, often clear or bluish, that forms when the duct of a small salivary gland on the inside of the lip is damaged; Cleveland Clinic writes that it most often appears on the inside of the lower lip and is mostly linked to lip biting. It raises a single spot, not the whole lip. A bee or wasp sting leaves a small mark where the sting went in and a painful swelling. Swelling after an injury has an obvious cause and usually comes with bruising. An abscess from a tooth can also make the face swell; this swelling is painful and warm, and is usually preceded by toothache.

The pictures in the first list are not emergencies, but they need a clinician's assessment. If even one of the signs in the second list is present, do not wait, and do not drive yourself to hospital.

The order starts with danger: first make sure the airway is safe, then look for the cause. The steps below cover both what you do at home and the route the clinician will follow.

1. 1

   Check for the emergency signs first

   Is your tongue getting thicker, is your voice becoming hoarse, can you swallow, is your breathing comfortable, do you feel dizzy? If any of these applies, or the lip has swollen suddenly, call 112. The NHS says not to drive yourself to A&E. For anaphylaxis, the NHS steps are: use an adrenaline auto-injector if you have one, call an ambulance, lie down (with your shoulders raised, or sitting up slowly, if you are short of breath), and do not stand up or walk, even if you feel better.

2. 2

   Record the time and take a photo

   Because the swelling is temporary, the doctor often never sees it. Photograph with your phone the time the swelling started, its largest size and the time it went down. If there are hives, photograph them too; whether or not there are hives separates the causes the doctor will consider from the start.

3. 3

   Write down the last 24 hours

   What did you eat, did you take a new medicine or painkiller, were you stung by an insect, did you have a dental procedure, did you bite your lip? MSD lists aspirin and other non-steroidal anti-inflammatory painkillers (NSAIDs), ACE inhibitors, some opioids, insect stings, eggs, fish, shellfish, nuts and fruit among the common triggers.

4. 4

   Take your medicine boxes to the doctor

   Take the box or a photo of every medicine you use. If the name of your blood pressure medicine ends in -pril, mention it specifically, even if you have been taking it for years. The decision and any change belong to the doctor who prescribed it.

5. 5

   If it keeps happening, ask for the right tests

   If the swelling has happened more than once and there are no hives, or there is a family history of similar swelling, ask your GP or an allergy and immunology specialist whether they will request blood tests for hereditary and acquired angioedema. MSD writes that doctors do these tests in this situation.

6. 6

   If a blister or firmness remains on the lip, show your dentist

   A blister that stays in one spot and has not gone down within days may be a mucocele. A swelling that has lasted for weeks, is hardening or forms an ulcer should be seen by a dentist or an oral and maxillofacial surgeon; if needed, a sample of tissue is taken and examined (a biopsy).

There is no single treatment for lip swelling; what is done depends on the cause of the swelling and whether it threatens the airway.

The points below are decisions that lead to angioedema getting worse, or to its cause going unfound for years.

The time depends on the cause. The course below is for the usual course of angioedema; the plan of the clinician treating you takes priority.

1. The first hours

   Allergic swelling starts soon after contact with the trigger; the NHS writes that the symptoms of anaphylaxis usually start within minutes. In the ACE inhibitor study, the patients who needed an airway intervention had mostly come to A&E within 4 hours of the symptoms starting; in other words, rapidly progressing swelling is the more dangerous kind.

2. After treatment for anaphylaxis

   The NHS writes that people usually stay in hospital for 2 to 12 hours, and sometimes need to stay longer. That is why observation continues even after the symptoms have passed.

3. If a medicine is the cause

   MSD writes that symptoms usually subside within 24 to 48 hours of stopping an ACE inhibitor. If the same medicine is continued, the swelling is expected to come back.

4. Mucocele and injury

   Most mucoceles burst and go down on their own; if one keeps coming back, it needs removing. Swelling from a bite or a blow usually goes down within days.

We do not give a figure here, because behind lip swelling there may be a mucocele that goes away on its own, or anaphylaxis needing observation in hospital. These are the items that determine the scope:

Whether the airway is involved

Swelling confined to the lip and swelling involving the tongue and throat need completely different levels of care.

Whether the swelling recurs

A one-off swelling with an obvious cause often needs no tests; recurring swelling without hives needs blood tests and specialist follow-up.

The type of cause

An allergy, a medicine, an inherited condition and a blister on the lip are the field of different specialists and mean different treatments.