Aging at the cellular level is characterized by oxidative stress, inflammation, and cell senescence. An extract of the brown seaweed Ascophyllum nodosum rich in phlorotannins has been studied for its inhibitory activity against oxidative stress, inflammation, and senescence. A. nodosum extract at 0.2 % prevented tBHP-induced reactive oxygen species production (evaluated using the H2DCF-DA test in cytofluorometry) in epithelial cells and LPS-induced TNF-α and IL-6 release (evaluated using ELISA technique) in macrophages. A. nodosum extract also increased nuclear SIRT1 activity in epithelial cells. Altogether, these beneficial cellular effects of phlorotannin-rich A. nodosum extract could be used in topical therapeutic formulations against aging.