If you have spent any time shopping for moisturizers, you have probably seen the word “ceramides” printed across bottles, jars, and skincare advertisements. They are often marketed as the ingredient your skin barrier desperately needs. There is actually solid biology…

Your moisturizer can work beautifully in July and suddenly feel useless in January. Or perhaps your skin feels comfortable outdoors during a humid summer, only to become tight after spending eight hours in an air-conditioned office. That is not necessarily…