Cosmetic composition comprises: a red algae extract (I) comprising an association of floridoside at 25-50 wt.% and isethionic acid at 10-25 wt.% with a mass ratio of 1:5; and a carrier. An independent claim is included for the red algae extract (I). ACTIVITY : Dermatological. MECHANISM OF ACTION : Heat shock protein 70 modulator. The ability of (I) modulate heat shock protein was tested using biological assays. The results showed that (I) significantly improved the synthesis of heat shock protein 70 in chemical stress.