I will review recent work on the application of Ward Identities (WI) and Effective Theories in the context of the QCD transition. In particular, thermal resonances such as $f_0(500)$ and $K_0^*(700)$, generated within Unitarized Chiral Perturbation Theory scattering at finite temperature, play a key role regarding chiral symmetry restoration and its interplay with $U(1)_A$ restoration, a fundamental problem to understand the nature of the transition. I will concentrate on several observables, such as susceptibilities and screening masses, for which the effective theory framework yields compelling results, in agreement with lattice simulations on the QCD phase diagram.
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