  We make a thermal analysis of the light scalar susceptibilities using
SU(3)-Chiral Perturbation Theory to one loop taking into account the QCD source
of isospin breaking (IB), i.e corrections coming from $m_u\neq m_d$. The value
of the connected scalar susceptibility in the infrared regime, the one relevant
when approaching chiral symmetry restoration, and below the critical
temperature is found to be entirely dominated by the $\pi^0-\eta$ mixing, which
leads to model-independent $\mathcal{O}(\epsilon^0)$ corrections, where
$\epsilon\sim m_d-m_u$, in the combination $\chi_{uu}-\chi_{ud}$ of flavour
breaking susceptibilities. We also present preliminary results for the
corrections to the real part of the pion self-energy at nexst-to-leading order
in SU(2)-Chiral Perturbation Theory taking into account electromagnetic
interaction. The zero and finite temperature results for the charged and
neutral pions are given in terms of the three-momentum of the external pion;
and their difference is calculated to this order stressing the fact that, at
low and moderate temperature, the mass splitting $M_{\pi^\pm}-M_{\pi^0}$ grows
with temperature for, at least, non-zero charged pion mass running inside the
loops.
