Skin barrier dysfunction is linked to allergy, suggesting that keratinocyte status is critical during its induction; the mechanisms remain largely elusive. Exosomes transfer cargo to distant cells to alter their function; interest in exosomes is growing as they can be used in diagnostics and therapy. Aberrantly differentiating keratinocytes increase secretion of exosomes which differ from normal vesicles; we hypothesise this could promote Sensitisation to allergens. This interdisciplinary study will determine how keratinocytes communicate with immune cells via exosomes to induce allergy or tolerance. We will assess the effects of exosomes on antigen presenting cells, their contribution to T cell responses in health and disease, and characterise activating/tolerogenic exosomes incl. by cutting-edge super-resolution imaging. The study will inform on communication between body barriers and immune cells, offering incremental advance towards novel diagnostic and therapeutic tools.