延迟性过敏反应（Delayed type hypersensitivity），又称第四型过敏反应（Type IV hypersensitivity），为一种细胞媒介反应。发病机制是人体对食物中抗原物质产生的免疫反应所致。延迟性过敏反应的发生率很高，据统计，45%的人群会对某一种或几种食物产生反应。这种过敏反应发病缓慢，又称为隐藏性过敏；一般于进食致敏食物后24小时后或数日后出现症状，因此延迟性过敏的自我诊断相当困难。延迟性过敏反应可于人的各个年龄阶段出现。

辅助T细胞会辨识第二型MHC分子中的抗原。此反应中的抗原呈现细胞为巨噬细胞，巨噬细胞会分泌IL-12，会刺激T_h1细胞增生。而辅助T细胞则会分泌IL-2和干扰素-γ。因此诱导产生更多T_h1细胞因子。此时细胞毒性T细胞会被活化，刺激摧毁目标细胞，同时巨噬细胞会释放水解酶，在表面呈现胞内抗原，并形成多核巨细胞。

Type 4 hypersensitivity is often called delayed type hypersensitivity as the reaction takes two to three days to develop. Unlike the other types, it is not antibody mediated but rather is a type of cell-mediated response.

CD4+ helper T cells recognize antigen in a complex with Class II major histocompatibility complex. The antigen-presenting cells in this case are macrophages that secrete IL-12, which stimulates the proliferation of further CD4+ T_h1 cells. CD4+ T cells secrete IL-2 and interferon gamma, further inducing the release of other T_h1 cytokines, thus mediating the immune response. Activated CD8+ T cells destroy target cells on contact, whereas activated macrophages produce hydrolytic enzymes and, on presentation with certain intracellular pathogens, transform into multinucleated giant cells.