I've been diagnosed with a cow's milk protein as an adult (blood test) and have been avoiding all sources of dairy since.
I've not worried too much about tablets saying they contain lactose, because I thought that the chances that they were contaminated with cow's milk protein were fairly small. As such, I've been taking cetirizine off and on all summer for hayfever, and it seemed to be fine, despite containing lactose.
However, I recently bought another brand, even cheaper than the normal cheapo brand that I have been using. And I am getting some hives again. It could be other things as well, but one of the things I wondered was whether certain brands of tablets are more or less likely to use lactose that was contaminated with cow's milk protein (i.e., do they get it from a different source/country/etc with different regulations? do they use a cheaper form? do some places use synthetic lactose whilst others use lactose actually derived from cow's milk? do some use lactose derived from other milk besides cows? does the amount/quality of lactose vary from batch to batch etc). I can't find any information on this sort of detail anywhere.
It's not a huge deal, but I'm just curious. I can't figure out what else in my diet might have changed or was new in the past week, apart from these. I'll go back and try another brand, but my symptoms are a bit hit and miss anyway that it's not going to be a perfectly controlled trial anyway.
I originally had fexofenadine, which I think is lactose-free, but I keep running out and the surgery doesn't give me a repeat prescription; and also I had found that zirtek was better for my eyes, so I thought I'd just buy it myself until I can get more fexofenadine.