Day moisturizers tend to be lighter and nowadays they usually contain SPF. Night creams don't contain SPF (which does make them feel different) and are often heavier and more hydrating. Anti-aging night creams may contain higher levels of active ingredients since they are specifically intended to be worn at night to minimize irritation from UV exposure. Of course, they are many anti-aging day creams available as well. But if you find that your anti-aging day cream is irritating, you may want to switch to a night cream and stick to a regular moisturizer for day use. Also, be sure to look for the ingredients mentioned earlier (in particular, retinol and retinyl acetate) since they can be especially irritating when worn during the day.