Immunotherapy is a treatment for patients with type I-mediated allergic diseases. Molecular forms of allergen-specific immunotherapy (AIT), based on inducing immunological tolerance characterized by increased IL-10, TGF-β, and IgG4 levels, and Treg cell are continuously emerging to improve the efficacy of the treatment, shorten the duration of protocols, and prevent any side effects. This review covers the recent progress in AIT and routes of antigen administration. Classical immunotherapy uses allergen extracts obtained from natural sources. Limitations of the uses of these extracts, such as sensitizations with nonspecific agents, can be avoided using purified components, hypoallergenic recombinant proteins, and vaccines based on peptides (epitopes). However, these molecules have low immunogenicity requiring new carriers or more effective adjuvants. Vaccines based on carrier-bound B-cell epitope-containing peptides and the constructions of allergens coupled to virus-like particles (VLPs) are under evaluation. The possibility of vaccinating with DNA encoding the allergen to obtain an allergen-specific Th1 and IgG response is in development and the success of messenger ribonucleic acid (mRNA) vaccines against severe acute respiratory syndrome Coronavirus 2 must encourage as well the re-exploration of mRNA vaccine platform for innovative AIT.