Why are antihistamines useful for treating many IgE-mediated allergic reactions but not effective in treating?

well, lets see an example.

a dog shitted.

that dog **** smelly.

somebody covered that dog **** with a plastic and cleaned it up.

smelly gone.

dog = allergen

dog **** = Histamine

somebody = antihistamine

smelly gone = allergic reaction stopped

obviously, as long as there is a dog (allergen), dog **** (allergic reaction/histamine) can be happened.

Antihistamines are only symptomatic treatment for it.

To treat allergic reactions, you need to keep away from allergen.

No treatment.

(pardon me for my example)

Ige Mediated Allergies

Antihistamines are only effective against histamine mediated immunity, the bulk of which show symptoms we know as allergies. Cellular immunity and other immunoglobulin mediated immunity would not be affected by the use of anti-histamines.