Episodes of HAE often occur without an obvious trigger. However, in some cases, a cause can be identified.

For instance, infections, minor injuries and mechanical stimuli such as pressure can induce an attack. Dental procedures or surgery to remove the tonsils are particularly critical, as they can cause swelling in the larynx. Emotional and mental stress can also trigger an attack.
Hormonal factors are another known cause of HAE attacks. For example, the frequency of episodes can be higher in women taking products containing estrogen (the “pill”), products for menopausal complaints or who have their menstruation.

A class of blood pressure lowering drugs known as ACE (angiotensin-converting enzyme) inhibitors are contraindicated in HAE patients as they have also been shown to trigger HAE attacks in some patients. HAE patients should, therefore, avoid taking this type of medication.