Most food allergies announce themselves within minutes. Alpha-gal syndrome does not, and that single difference explains why people spend years being tested for the wrong things before anyone connects a middle-of-the-night reaction to a burger eaten at dinner.
The syndrome is an allergy to a sugar molecule called galactose-alpha-1,3-galactose, found in the tissue of most mammals but not in humans. People acquire it after a tick bite, most often from the Lone Star tick in the United States, when the tick's saliva introduces the molecule through the skin and the immune system responds by building antibodies against it. Beef, pork, lamb, venison and goat can then trigger a reaction. So can dairy, gelatin, some medication capsules and certain skin care products, depending on severity.
