Large polymeric nanoparticles (200–500 nm) can rapidly diffuse through fresh human cervicovaginal (CV) mucus when coated with polyethylene glycol (PEG), despite the mucus's viscoelastic properties. This finding challenges the prevailing belief that large nanoparticles are too big to move efficiently through mucus. The study used high-speed multiple-particle tracking to measure the transport rates of various-sized and surface-modified particles in CV mucus. Results showed that PEG-coated 200- and 500-nm particles had effective diffusion coefficients (D_eff) only 4- to 6-fold lower than in water, while 100-nm particles had D_eff 200-fold lower. Larger particles were less hindered by mucus, suggesting that PEG coating reduces interactions with mucus components, enabling faster transport. The study also found that the effective mesh spacing in CV mucus is larger than previously thought, possibly including pores larger than 500 nm. These findings indicate that large PEG-coated nanoparticles can penetrate physiological mucus, offering potential for mucosal drug delivery. The results highlight the importance of particle size, surface chemistry, and concentration in mucus transport, and suggest that PEGylation can enhance drug delivery efficiency by allowing particles to move more freely through mucus barriers. The study also emphasizes the need for further research into the role of particle concentration and mucus composition in transport mechanisms.Large polymeric nanoparticles (200–500 nm) can rapidly diffuse through fresh human cervicovaginal (CV) mucus when coated with polyethylene glycol (PEG), despite the mucus's viscoelastic properties. This finding challenges the prevailing belief that large nanoparticles are too big to move efficiently through mucus. The study used high-speed multiple-particle tracking to measure the transport rates of various-sized and surface-modified particles in CV mucus. Results showed that PEG-coated 200- and 500-nm particles had effective diffusion coefficients (D_eff) only 4- to 6-fold lower than in water, while 100-nm particles had D_eff 200-fold lower. Larger particles were less hindered by mucus, suggesting that PEG coating reduces interactions with mucus components, enabling faster transport. The study also found that the effective mesh spacing in CV mucus is larger than previously thought, possibly including pores larger than 500 nm. These findings indicate that large PEG-coated nanoparticles can penetrate physiological mucus, offering potential for mucosal drug delivery. The results highlight the importance of particle size, surface chemistry, and concentration in mucus transport, and suggest that PEGylation can enhance drug delivery efficiency by allowing particles to move more freely through mucus barriers. The study also emphasizes the need for further research into the role of particle concentration and mucus composition in transport mechanisms.