Aerosol siRNA delivery to the lungs. (A) pulmonary delivery of naked or siRNA nanocarriers, (B) Carrier-based delivery of siRNA cellular uptake. The aerosolized formulation of siRNA and use of appropriate device delivers siRNA by inhalation, intratracheal, or intranasal delivery to the human or animal lung. Once the siRNA carriers reach the lower respiratory tract, they may reach target cells and become internalized through endocytosis. Carriers capable of endosomal escape avoid degradation in the lysosome and release free siRNA within the cytoplasm. The RNAi pathway may then be initiated, ultimately leading to mRNA degradation and gene silencing.