We study the dynamics of a tracer particle (TP) on a comb lattice populated by randomly moving hard-core particles in the dense limit. We first consider the case where the TP is constrained to move on the backbone of the comb only, and, in the limit of high density of particles, we present exact analytical results for the cumulants of the TP position, showing a subdiffusive behavior ∼ t 3/4 . At longer times, a second regime is observed, where standard diffusion is recovered, with a surprising non analytical dependence of the diffusion coefficient on the particle density. When the TP is allowed to visit the teeth of the comb, based on a mean-field-like Continuous Time Random Walk description, we unveil a rich and complex scenario, with several successive subdiffusive regimes, resulting from the coupling between the inhomogeneous comb geometry and particle interactions. Remarkably, the presence of hard-core interactions speeds up the TP motion along the backbone of the structure in all regimes.Subdiffusive motion of tracer particles in crowded media, e.g. biological cells, is widespread. Among the possible microscopic scenarios leading to this sublinear growth with time of the mean square displacement (MSD), the existence of geometric constraints related to the complexity of the environment plays an important role [1,2]. In this context, the comb model (see Fig. 1), in which a single particle moves on a two-dimensional space with the constraint that steps in the x direction are only allowed when the y coordinate of the particle positions is zero, has attracted considerable attention because of its simplicity and ability to reproduce subdiffusive behaviors of disordered systems [3].Comb-like structures have indeed been introduced as a first step to model diffusion in more complicated fractal structures like percolation clusters, the backbone and teeth of the comb representing the quasilinear structure and dangling ends of percolation clusters [4]. The particle can spend a long time exploring a tooth, which results in a subdiffusive motion along the backbone with x 2 (t) ∝ t α with α = 1/2. Since, numerous results have been obtained for this model [5][6][7][8][9][10][11][12], including the determination of the occupation time statistics [13], of mean first-passage times between two nodes of a finite comb [14] or the case of fractional Brownian walks on comb-like structures [15].In parallel, the comb model has been invoked to account for transport in real systems like spiny dendrites [10], diffusion of cold atoms [16] and mainly diffusion in crowded media like cells [17]. However, all existing studies have focused on single-particle diffusion, and interactions between particles have up to now been completely left aside. As an elementary model for diffusion of particles under short-range repulsive forces, we consider here excluded-volume interactions (EVIs) and focus on their impact on tracer dynamics on comb-like structures.From a theoretical point of view, lattice systems of interacting particles represent a protot...