Steeping your tea in these bags releases billions of nanoparticles of plastic into our teacup and thus, our bodies. In addition to that, the “paper” packaging these tea bags usually come in, has a plastic liner as well.
Compostable tea bags may exist, but they may still release plastic into the environment nonetheless. Brewing loose-leaf tea means no extra single-use materials and often comes in reusable and refillable tins.