Dendritic cells are a type of white blood cell that specializes in identifying foreign substances. When these cells recognize substances that can be harmful to the body, they activate and regulate the other parts of the immune response to handle the foreign substance. The immune system’s main task is to protect the body from attacks by various types of microorganisms, such as bacteria and viruses, but sometimes it reacts to other substances, which can lead to an allergic reaction. When dendritic cells recognize a substance as foreign, they are activated and change their function and appearance. These changes start with expression regulation of various genes; this can be measured using various techniques, and this is what serves as the foundation for the GARD test’s capability to differentiate between allergenic chemicals and non-allergenic chemicals.