HAE Day is observed worldwide every May 16 to educate the public about hereditary angioedema (HAE), a rare genetic disorder that causes recurrent episodes of severe swelling. Established in 2002 by HAE International (HAEi), a global non-profit network of patient organizations, the day aims to advocate for early diagnosis, improved care, and accessible treatment for those affected by HAE. Activities on this day include learning about the disorder, attending events organized by national HAE organizations, participating in the annual HAE Day Activity Challenge, and sharing information on social media using the hashtag #HAEDay. HAE affects approximately 1 in 10,000 to 1 in 50,000 people and can lead to dangerous swelling in various parts of the body, particularly the gastrointestinal and respiratory tracts. The day serves to highlight the importance of understanding the condition, as many patients face misdiagnosis and delayed treatment due to its rarity and the unfamiliarity of many healthcare professionals with its symptoms.