Desensitisation and antihistamines

[Aparecium]

I have PMLE and generally try to desensitise every year, either through phototherapy or by gradual exposure. It doesn't always work, in which case I take antihistamines. Once I've reacted, desensitisation doesn't improve matters and I end up on antihistamines for several months.

Does anybody know whether taking antihistamines prevents desensitisation?

Hi where do you get that done please?
Just researching about desensitisation atm for me and my child (5yo). Not sure if health insurance will cover this as they claim they don't cover allergies.

NHS.

I was being seen by a dermatologist for an unrelated problem. She explained that I also had PMLE, and suggested I try phototherapy.