Final answer:
Skin thickening in SICCT is caused by an allergic reaction where the immune system responds to the tuberculin antigen used in the test, leading to inflammation and thickening of the skin.
Step-by-step explanation:
The question asks what causes skin thickening in SICCT. SICCT stands for Single Intradermal Comparative Cervical Tuberculin test, which is a type of skin test used to diagnose bovine tuberculosis. Skin thickening in the context of diagnostic tests like SICCT is typically due to an allergic reaction, where the body's immune system reacts to the tuberculin antigen introduced into the skin.
This allergic reaction leads to inflammation and an increase in the number of immune cells in the area, which manifests as skin thickening. This response is a delayed-type hypersensitivity reaction, similar to what is seen in the tuberculin skin test used in humans to diagnose tuberculosis.