st johns wort interaction with antihistamine

[Realitea]

I've got a horrible itchy rash all over after colouring my hair yesterday. It pops up in one place, goes away then another appears somewhere else. I'm currently taking st johns wort so i dont know if there are any antihistamines that are safe for me.
What else can I do?
I'm worried i'll puff up like a balloon!

[sadie9]

Think it just might make the antihistamine less effective. St John's Wort can cause breakthrough bleeding with the Pill though I've just been reading so may make them less effective too. Didn't know that. Is there a leaflet with the St John's Wort?

[Footle]

Go and talk to a pharmacist.

[Realitea]

Ok I spoke to a pharmacist and she said cetirizine is ok so I had one and it's helped a bit. However now I have pin prick spots under my skin all over! Might have had it before I don't know but it's really putting me off this St. John's wort !