The TB skin test is administered on which skin layer?

• A. Subcutaneous
• B. Epidermis
• C. Dermis
• D. Hypodermis

Answer: (B)

The TB skin test is given intradermally, placing the antigen in the dermal layer of the skin. The dermis is where the localized immune response develops: it contains immune cells like macrophages and dendritic cells that present the tuberculin protein to T cells, producing a delayed-type hypersensitivity reaction that shows up as induration within 48–72 hours. The epidermis, by contrast, is the outermost layer with few blood vessels and fewer resident antigen-presenting cells, so injecting there wouldn’t yield the reliable, measurable reaction used for interpretation. Subcutaneous or deeper hypodermal tissue would alter diffusion and reading, not producing the characteristic induration used to assess exposure.