Once histamine is activated the response is generalized so that is why food allergies can also manifest as runny eyes or nose, itchy eyes or nose, rash or hives, itchy skin etc. gastrointestinal symptoms include nausea, vomiting, diarrhoea or abdominal cramps, burning in the chest. Respiratory symptoms of wheeze, shortness of breath, itchy throat etc can occur with any allergy, a bronchodilator such as salbutamol can be used. There are also neurological symptoms and so on.
H1 blockers will act at all sites o histamine action but have limited effectiveness against severe cardio respiratory effects including bronchoconstriction, blood vessel dilation which causes hypotension (low blood pressure) and poor pump function of the heart. These are treated by epinephrine and fluids. Fluids alone are ineffective because blood vessels get leaky and that causes edema or swelling in all kinds of tissues including the airway. Therefore epinephrine first to decrease the permeability of blood vessels which contributes to the swelling.
