Final answer:
A Contact irritant is most likely to produce dermatitis. Contact dermatitis occurs when a previously sensitized individual is re-exposed to an allergen, leading to an immune response with inflammatory skin lesions.
Step-by-step explanation:
The toxic substance most likely to produce dermatitis is a Contact irritant. Exposure to substances such as poisons ivy oils, heavy metals like nickel, or latex can cause contact dermatitis, which is a type IV hypersensitivity reaction. This occurs when a person has been previously sensitized to the substance. Upon re-exposure to the same allergen, memory T cells respond by producing inflammatory cytokines that stimulate other immune cells, such as macrophages and cytotoxic T cells, leading to the inflammatory lesions typical of dermatitis. Sensitizers such as poison ivy cause the skin reaction only after the immune system has been sensitized to the allergen during a prior exposure.
Other substances, such as mutagens, teratogens, and sensitizers, also interact with the body but cause different types of harm. Mutagens can cause mutations in the DNA of cells, while teratogens are agents that can disturb the development of an embryo or fetus. Sensitizers can indeed lead to allergic reactions, but a contact irritant is directly responsible for dermatitis upon exposure.