Dinitrochlorobenzene: A skin irritant that may cause dermatitis of both primary and allergic types. Contact sensitization with DNCB has been used as a measure of cellular immunity. DNCB is also used as a reagent for the detection and determination of pyridine compounds.Irritants: Drugs that act locally on cutaneous or mucosal surfaces to produce inflammation; those that cause redness due to hyperemia are rubefacients; those that raise blisters are vesicants and those that penetrate sebaceous glands and cause abscesses are pustulants; tear gases and mustard gases are also irritants.NitrobenzenesPhthalic Anhydrides: Phthalic acid anhydrides. Can be substituted on any carbon atom. Used extensively in industry and as a reagent in the acylation of amino- and hydroxyl groups.Skin Tests: Epicutaneous or intradermal application of a sensitizer for demonstration of either delayed or immediate hypersensitivity. Used in diagnosis of hypersensitivity or as a test for cellular immunity.Dermatitis, Photoallergic: A delayed hypersensitivity involving the reaction between sunlight or other radiant energy source and a chemical substance to which the individual has been previously exposed and sensitized. It manifests as a papulovesicular, eczematous, or exudative dermatitis occurring chiefly on the light-exposed areas of the skin.Local Lymph Node Assay: The local lymph node assay (LLNA) is an alternative method for the identification of chemicals that have the ability to cause skin sensitization and allergic contact dermatitis. Endpoints have been established so fewer animals are required and less painful procedures are used.Dermatitis, Allergic Contact: A contact dermatitis due to allergic sensitization to various substances. These substances subsequently produce inflammatory reactions in the skin of those who have acquired hypersensitivity to them as a result of prior exposure.Hypersensitivity, Delayed: An increased reactivity to specific antigens mediated not by antibodies but by cells.Dermatitis, Contact: A type of acute or chronic skin reaction in which sensitivity is manifested by reactivity to materials or substances coming in contact with the skin. It may involve allergic or non-allergic mechanisms.Ear, External: The outer part of the hearing system of the body. It includes the shell-like EAR AURICLE which collects sound, and the EXTERNAL EAR CANAL, the TYMPANIC MEMBRANE, and the EXTERNAL EAR CARTILAGES.Immunity, Cellular: Manifestations of the immune response which are mediated by antigen-sensitized T-lymphocytes via lymphokines or direct cytotoxicity. This takes place in the absence of circulating antibody or where antibody plays a subordinate role.Haptens: Small antigenic determinants capable of eliciting an immune response only when coupled to a carrier. Haptens bind to antibodies but by themselves cannot elicit an antibody response.Allergens: Antigen-type substances that produce immediate hypersensitivity (HYPERSENSITIVITY, IMMEDIATE).Skin: The outer covering of the body that protects it from the environment. It is composed of the DERMIS and the EPIDERMIS.Lymphocyte Activation: Morphologic alteration of small B LYMPHOCYTES or T LYMPHOCYTES in culture into large blast-like cells able to synthesize DNA and RNA and to divide mitotically. It is induced by INTERLEUKINS; MITOGENS such as PHYTOHEMAGGLUTININS, and by specific ANTIGENS. It may also occur in vivo as in GRAFT REJECTION.