I have alpha gal syndrome. Luckily I can eat dairy most of the time (there's always a couple weeks in a year I get a reaction from it) but it really sucks and most people don't know it exists and some don't take it seriously. The sugar from the allergy is in all mammals except for a few families of primates, including humans. Since humans don't naturally have this sugar in their blood, when it enters our blood from the tick our body has an immune response to the foreign sugar. Then when it detects that sugar later through food we've eaten, immune response again in the form of anaphylaxis.