  Many new physics scenarios contain ultralight scalars, states which are
either exactly massless or much lighter than any other massive particle in the
model. Axions and majorons constitute well-motivated examples of this type of
particle. In this work, we explore the phenomenology of these states in
low-energy leptonic observables. After adopting a model independent approach
that includes both scalar and pseudoscalar interactions, we briefly discuss the
current limits on the diagonal couplings to charged leptons and consider
processes in which the ultralight scalar $\phi$ is directly produced, such as
$\mu \to e \, \phi$, or acts as a mediator, as in $\tau \to \mu \mu \mu$.
Contributions to the charged leptons magnetic and electric moments are studied
as well.
