Bethenny Frankel is swearing off hotel towels for good ... she claims towels are breeding grounds for bacteria, even at swanky resorts, and she's blaming them for the bacterial infection she contracted in St. Barts.

The 'RHONY' alum hopped on TikTok Thursday -- and revealed how she believes she ended up with a large rash spread across her face after a luxury New Year's getaway to the Caribbean.

Bethenny says there's no magical towel fairy that cleans towels the second they get dirty at hotels, even at the expensive resorts in St. Barts ... claiming dirty towels sit around with dirt, grime, sweat, food and all sorts of things on them before going in the washer.

She says her bacterial infection is all gone now ... and it sounds like she's going to bring her own towels and bed sheets the next time she checks in.

And if you thought towels were dirty ... wait until you hear what Bethenny has to say about makeup sponges.