Thymic stromal lymphopoietin (TSLP) is an important factor that affects the development of allergic diseases. Single nucleotide polymorphism of TSLP is closely related to the susceptibility, course and severity of allergic diseases. Following exposure to allergens, multiple signalling pathways in epithelial cells mediate TSLP expression and induce an immune cascade. TSLP affects epithelial physical barrier damage by inhibiting the expression of tight junctions, adhesion junctions and desmosomes and destroying the lipid layer. Two isomers of TSLP have antibacterial properties and can enhance the defence ability of the skin and mucosa. Moreover, TSLP plays a protective role by up-regulating the expression of tight junction proteins during early inflammation. In allergic diseases, TSLP participates in the proliferation and differentiation of various immune cells through the TSLP receptor pathway and releases pro-inflammatory and chemokine factors, thus mediating immune inflammation. Furthermore, TSLP is involved in airway remodelling in respiratory allergies by inducing fibrocyte migration and recruitment and promoting epithelial-mesenchymal transformation. Therefore, inhibition of TSLP may be a potential target for the treatment of allergic diseases. Research on biological agents targeted by TSLP is warranted for the treatment of allergic diseases in the future.