a - 4 what is an allergy?
b - 1 how does the immune system work?
c - how does allergic reaction occur?
d - 5 what does histamine do?
e - 6 what are the symptoms of allergy?
f - 2 what can you be allergic to?
g - 3 why do some people get allergies and not others?
h - 7 why has allergy increased?