Pseudoscalars appear frequently in particle spectra. They can be light if they appear as pseudo-Goldstone bosons from some spontaneously broken global symmetries with the decay constant f. Since any global symmetry is broken at least by quantum gravitational effects. all pseudoscalars are massive. https://www.spidertattooz.com/The-GelBottle-Inc-Gel-Polish-Audrey-67oz-p17921/