Marketing puff. There is nothing unusual in the product - certainly nothing that could be described as a “prebiotic” (whatever that is).
Avobenzone 3% (sunscreen), Homosalate 5% (sunscreen), Octisalate 5%
(sunscreen), Octocrylene 7% (sunscreen)
Water (La Roche-Posay Prebiotic Thermal Water), Glycerin, Silica,
Dimethicone, Niacinamide, PEG-100 Stearate, Glyceryl Stearate, Stearic
Acid, Stearyl Alcohol, Allantoin, Ceramide NP, Dimethicone/vinyl
Dimethicone Crosspolymer, Sodium Hydroxide, Myristic Acid, Myristyl
Alcohol, Palmitic Acid, Ammonium Polyacryloyldimethyl Taurate, Disodium
Edta, Capryloyl Glycine, Caprylyl Glycol, Citric Acid, Xanthan Gum,
T-butyl Alcohol, Cetyl Alcohol, Tocopherol
(La Roche-Posay Prebiotic Thermal Water is declared as water, nothing else. Just because it may be obtained from a geothermal source does not impart supernatural properties).