Why antihistamines can't do it all

[webslave]

Assuming you are one of those men whose mast cells are reacting chiefly to allergens, how come antihistamines help you but cannot completely cure you?

Here's the reason: antihistamines only de-activate or block one part of the range of chemicals mast cells release. Antihistamine drugs do not, however, block the action of prostaglandins and leukotrienes, which have similar effects to histamine.

[gunde]

Thats not entirely true if I'm not mistaken. Desloratadine for example blocks the H1 receptors and hence prevents the mast cells from degranulating and releasing any of the chemicals.
But since this blockage is far from 100% and there exists other mast cells triggers, the mast cells might degranulate and release those chemicals.

[webslave]

Histamine is released after the mast cells degranulate, not before. Antihistamines deal with the consequences of degranulation.

One effect antihistamines have is the inhibition of the histamine-mediated release of inflammatory mediators by leukocytes (Cuss 1999). Other antihistamine effects result in the neutralization of histamine, preventing it from binding and activating immune-related cells in the area.