The doubly-charged scalar often appears in Standard Model extensions motivated by perturbative mechanisms for neutrino mass generation. After briefly reviewing the models, I will focus on the corresponding low-energy effective field theory, the current constraints from flavour physics and the matching at the electroweak scale. The second part of the seminar will examine the status of current searches at the LHC and the discovery potential of the HighLumi LHC and of future e+e-colliders. I will show how these different bounds from low- and high-energy physics combine in a coherent picture.