sentence <-
    "active ingredients: avobenzone, octocrylene, octyl salicylate.
    other stuff inactive ingredients: water, glycerin, edta."

"avobenzone, octocrylene, octyl salicylate, water, glycerin, edta."

gsub("([:punct:][^:]*:)|^([^:]*:)", "", sentence)

[1] " avobe water, glycerin, edta."