What substance is injected into the patient's body to determine the cause of an allergy?

Allergen to which the patient is allergic

The correct option for determining the cause of allergy by injecting it into the patient's body is the allergen to which the patient is allergic.

Allergy testing involves introducing small amounts of suspected allergens into the patient's body to observe any allergic reactions. This can be done through various methods, such as skin prick tests or allergen-specific IgE blood tests. By introducing the allergen into the body, the immune system reacts if the person is allergic to that particular substance, causing localized allergic symptoms at the injection site.

IgG and IgE are types of antibodies produced by the immune system in response to allergens, but they are not directly injected into the patient's body for determining the cause of allergy.

Steroids, on the other hand, are medications that can be used to manage allergic reactions and reduce inflammation but are not injected for the purpose of determining the cause of the allergy.