Antihistamine

[Beanwood]

As @Jacqui-S mentioned there are first and second gen antihistamines available, The first gen went through the blood brain barrier leading to other receptor activity namely drowsiness. All have activity on H1 receptors. Anti acids work on H2 receptors in the gut.
Some antihistamines have a faster onset of action, which I why I personally like Benedryl (acrivastine) but I also then add in fexofendine (telfast 180 ) if I get a bee-sting. Telfast 180 really packs a punch, plus it doesn't cause drowsiness. I am not sure acrivastine is completely free of drowsy side effects. Although piriton (chlorphenamine) has been around the longest, it is still one of the most effective anti-histamines out there baring fexofenadine 180.

 

[Boogie]

I’m severely allergic to wasp stings and piriton is my first line of defence, ‘tho I do have an epipen in case things get serious.

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[Jacqui-S]

It makes sense to to start antihistamines as soon as possible because the act of more itching produces mode histamines so makes you more itchy.
Hence the so-called itch-scratch-itch cycle.

 

[FayRose]

Thanks to you all for your informative replies. They have helped me to decide how to deal with Molly's problems, with a heck of a lot more vital info. then I had previously. All very much appreciated.