Hi Bex. I read it is the protein casein. Milk has 2 proteins, casein and whey. When they make cheese, they separate the whey from the casein (at least mostly). So, ricotta cheese, which is whey cheese, may be ok. I don't know, though. It's probably worth doing some reading/surfing to find out if it's ok to have dairy products. I personally don't eat them anymore, for various reasons. I've also read that it's just milk that causes problems. And I've also read it's just the lactose.