Sizable neutrino self-interactions could exist and affect our understanding of large neutrino density environments. But if they are mediated by a light boson, i.e., have a long range, they might be extremely challenging to probe. In this work, we scrutinize how cosmology is well-suited to study them. In particular, we demonstrate that the energy density and equation of state of interacting cosmological neutrinos would diverge from the commonly assumed ideal gas form. Our results show that the current cosmological neutrino mass bound is fully avoided in the presence of a long range interaction, opening the possibility for a laboratory neutrino mass detection in the near future. We also demonstrate an interesting complementarity between neutrino laboratory experiments and the future EUCLID survey.