Immunotoxicology is that the dysfuntion of system due to exposure of organism to extrinsic factors. The system may be a target following exposure to a various group of xenobiotic including chemical pollutants, recreational drugs, ultraviolet and therapeutics. there's a well-established cause and effect relationship between suppression of the immune reaction and reduced resistance to infections. Xenobiotic exposure may end in stimulation of immune function. Xenobiotic can act as allergens and elicit hypersensitivity responses, or they will modulate hypersensitivity responses to other allergens. The immune dysfunction may take the shape of immunosuppression or alternatively, allergy or autoimmunity or any number of inflammatory-based diseases.. Immunotoxicity are often considered one among several distinct immunopathologies that include allergic disease, immunodeficiency and autoimmunity. In immunopathologies, the system responds to the agent as an allergen of low (hapten) or high relative molecular mass , that end in allergic dermatitis , food hypersensitivity or respiratory hyper-sensitivity. In immunodeficiency, the system acts as a passive target for the agent and this might cause increased incidence or severity of communicable disease . Autoimmunity which may be a break-down in self-tolerance occurs when an agent directly or indirectly induces an immune reaction to autologous constituents that end in pathological consequences.