 Abstract cellular membrane area is a key parameter for any living cell that is tightly regulated to avoid membrane damage. Changes in area to volume ratio are known to be critical for cell shape, but are mostly investigated by changing the cell volume via osmotic shocks. In turn, many important questions relating to cellular shape, membrane tension homeostasis and local membrane area cannot be easily addressed because experimental tools for controlled modulation of cell membrane area are lacking. Here we show that photo-switching an amphiphilic azobenzine can trigger its intercalation into the plasma membrane of various mammalian cells ranging from erythrocytes to myoblasts and cancer cells. The photoisomerization leads to a rapid, 250 to 500 milisacons, and highly reversible membrane area change, ca2% for erythrocytes, that triggers a dramatic shape modulation of living cells. This article was authored by Fabian Hogelsberger, Barty Vos, Andi Hofmeier, and others. We are article.tv, links in the description below.