HAE stands for hereditary angioedema, a rare genetic condition that causes recurring episodes of severe swelling in different parts of the body. It affects roughly 1 in 50,000 people and results from a problem with a specific blood protein that normally keeps inflammation in check. The swelling can appear in the hands, feet, face, abdomen, or throat, and episodes can range from uncomfortable to life-threatening.
What Happens in the Body
HAE is rooted in a deficiency or malfunction of a protein called C1 inhibitor (C1-INH). Under normal circumstances, C1-INH acts as a brake on several inflammatory pathways in the blood. When that brake is weak or missing, the body overproduces a compound called bradykinin, which makes blood vessel walls leak fluid into surrounding tissues. The result is deep, often painful swelling that can last several days before resolving on its own.
This mechanism is different from a typical allergic reaction. Allergic swelling involves histamine, which is why antihistamines and epinephrine work for allergies. HAE swelling is driven by bradykinin, so standard allergy treatments have no effect. This distinction matters because people with HAE are sometimes misdiagnosed with allergies for years before getting the correct diagnosis.
The Three Types of HAE
Type I is the most common form, accounting for about 85% of all cases. People with Type I produce too little C1-INH protein overall. Type II is less common and occurs when the body produces normal or even elevated amounts of C1-INH, but the protein doesn’t work correctly. Both types are caused by mutations in a gene called SERPING1, with hundreds of different mutations identified so far. Type I mutations occur throughout the gene, while Type II mutations tend to cluster in a specific section called exon 8.
A third category, sometimes called HAE with normal C1 inhibitor, exists as well. In these cases, C1-INH levels and function test normally, making diagnosis more challenging. This type may involve mutations in other genes that affect the same bradykinin pathway.
HAE follows an autosomal dominant inheritance pattern, meaning a child needs to inherit only one copy of the mutated gene from one parent to develop the condition. Each child of an affected parent has a 50% chance of inheriting it.
What an Attack Feels Like
Swelling episodes typically develop over several hours and can last two to five days. The location varies from person to person and from attack to attack. Common sites include the hands, feet, face, and genitals. When swelling hits the intestinal wall, it causes intense abdominal pain, nausea, vomiting, and sometimes diarrhea. These abdominal attacks are frequently mistaken for appendicitis or other surgical emergencies, and some patients undergo unnecessary operations before HAE is recognized.
The most dangerous attacks involve the throat. Swelling in the airway can obstruct breathing and is a medical emergency. Early signs include a feeling of tightness in the throat, voice changes, or difficulty swallowing. Throat attacks progress over hours rather than minutes, which provides a window for treatment, but they require immediate medical attention.
Common Attack Triggers
Emotional stress is the most frequently reported trigger. Stress hormones like adrenaline and cortisol can spark a surge of inflammation that sets off the bradykinin cascade. Physical trauma is another major trigger, including minor injuries, surgeries, and dental procedures. Dental work is a particularly well-known culprit because of the mechanical stress it places on tissues near the airway.
Hormonal fluctuations play a significant role, especially for women. Monthly menstrual cycles, pregnancy, and menopause can all influence attack frequency and severity. This is part of the reason HAE tends to be more severe in women than men. Medications containing estrogen, such as certain birth control pills and hormone replacement therapy, can worsen attacks. ACE inhibitors, a common class of blood pressure medications, are also known to trigger episodes because they interfere with bradykinin breakdown.
Exercise and repetitive motions can provoke swelling too. Activities that put sustained pressure on the same body part, like working with hand tools or typing for extended periods, sometimes trigger localized attacks in that area.
How HAE Is Diagnosed
The most reliable and cost-effective initial screening test is a blood measurement of a protein called C4. C4 levels drop during HAE attacks and usually remain low even between episodes. If C4 is low, further testing measures C1-INH levels and C1-INH function to distinguish between the types.
In Type I, both C1-INH levels and C4 levels come back low. In Type II, C1-INH levels appear normal or high, but a functional test reveals the protein isn’t working properly, and C4 remains low. HAE with normal C1 inhibitor is harder to pin down because all standard blood tests may come back normal, and diagnosis often relies on family history and genetic testing.
Because HAE is rare, the average delay between first symptoms and correct diagnosis can stretch for years. Many patients are initially treated for allergies, irritable bowel syndrome, or anxiety before someone orders the right blood tests.
Treating Acute Attacks
Several treatments can stop an HAE attack once it starts. For decades, the only options were injections or IV infusions. These include medications that replace the missing C1-INH protein directly and others that block either bradykinin itself or the enzyme that produces it. Most of these can be self-administered at home after proper training, which means patients don’t always need an emergency room visit for a non-throat attack.
A significant recent development is the first oral on-demand treatment for acute attacks. This pill is designed to be taken at the first sign of swelling, providing an alternative to needles. For many patients, having an oral option lowers the barrier to early treatment, which is important because attacks are easier to control when caught early.
Preventing Attacks Long-Term
People who experience frequent or severe attacks may benefit from long-term preventive therapy, sometimes called prophylaxis. First-line options include regular infusions or injections of C1-INH replacement and a newer injectable medication that targets the bradykinin pathway further upstream. These preventive treatments can dramatically reduce the number of attacks per year.
The decision to start preventive treatment isn’t based on rigid criteria. It depends on how often attacks occur, how severe they are, where they tend to strike, and how much they disrupt daily life. Someone who has a few mild hand swellings per year may manage fine with on-demand treatment alone, while someone experiencing weekly abdominal attacks or any history of throat involvement would likely benefit from ongoing prevention.
For HAE with normal C1 inhibitor, preventive options differ. Progestin-based hormonal therapy and antifibrinolytic medications are typically considered first, since the standard C1-INH replacement therapies target a deficiency that doesn’t exist in this type.
Living With HAE
HAE is a lifelong condition with no cure, but modern treatments have transformed the outlook. Before effective therapies existed, throat attacks carried a significant mortality risk. Today, with on-demand treatments available for home use and effective preventive options, most people with HAE can live full, active lives.
Practical management involves keeping on-demand medication accessible at all times, wearing medical identification, and informing dentists and surgeons about the condition before any procedures. Many specialists recommend pre-treatment before dental work or surgery to reduce the risk of a procedure-triggered attack. Avoiding known personal triggers, particularly estrogen-containing medications and ACE inhibitors, is also a straightforward way to reduce attack frequency.