During an allergic condition,which hormone is secreted?

Assertion : Histamine is involved in allergic and inflammatory reactions.
Reason : Histamine is a vasodilator.

Hypersensitivity towards any foreign material or particle is known as

Which chemicals cause allergy and how can the cause of allergy be determined?

Which of the following diseases is caused due to an allergic reaction?

$A$ person shows strong unusual hypersensitive reactions when exposed to certain substances present in the air. Identify the condition. Name the cells responsible for such reactions. What precaution should be taken to avoid such reactions?