IgG4 antibodies are associated with non-atopic or "delayed" food reactions that can worsen or contribute to many different health problems. These reactions are considered the most common form of immunologically mediated food intolerance.
An IgG4 response to food is actually more common than the IgE response, which causes an immediate reaction. These reactions are more difficult to notice since they can occur hours or even days after consumption of an offending food. In some cases, a person's reaction to a food may occur several days after eating the offending food and the link between the food and their symptoms may not be connected. These "hidden" food allergies are caused by increasing blood levels of IgG4 antibodies in reaction to specific foods.