https://www.nyallergy.com/lychee-allergy/

Lychee allergy is frequently linked to Latex-Fruit Syndrome. This occurs because the proteins in lychee are structurally similar to the proteins found in natural rubber latex. Additionally, individuals with a birch pollen allergy may experience cross-reactivity with lychee due to similar protein structures (specifically the Bet v 1 related proteins).

In addition to latex, those who are allergic to lychees may also experience cross-reactive symptoms with these plant foods:

Mango
Kiwi
Papaya
Sunflower seeds
Mugwort pollen
Birch pollen

純粹係因為有致敏源，某D人食咗會腫／發炎。以前老人家會當呢啲係上火、熱氣