H1 antihistaminics afford benefit in a number of conditions. All of the following conditions are benefited by antagonism of histamine :
In common cold , excessive secretions (like rhinorrhoea) are due to cholinergic overactivity. First generation antihistaminics possess anticholinergic propey and therefore are effective for common cold. On the other hand, all other conditions are allergic and reare benefited by antagonism of H1 receptors.
Dermographism
Insect bite
Common cold
Seasonal hay fever
Histamine, 5-HT and PGs