Sensitive, in the medical sense, describes a person who reacts unexpectedly to an allergen or drug because earlier exposure created antibodies against it. The first encounter sensitised the immune system silently; the next triggers symptoms ranging from rashes and wheezing to full anaphylaxis. Food examples include the child sensitised to milk protein who later reacts to a trace in a biscuit, or the adult who becomes sensitive to shellfish after years of safe eating. Sensitivity differs from intolerance: it is immune-mediated, dose-independent in the extreme, and potentially life-threatening. Diagnosis combines history with specific IgE blood tests or skin-prick testing. For sensitive individuals, labelling, vigilance, and emergency medication are daily necessities, not precautions.