Since I don't much use lipsticks, I find them lasting me for years. However, like with every product they are supose to get expired. Luckily, if I use a lipstick which is expired my lips start to chaff immediately so I know that the product is expired otherwise I wouldn't know how to fnd out if the lipstick has expired. That's when I replace it. Is there a way to detect an expired lipstick as they have no dates on them? When do you replace your lipsticks?
It takes me 4 lipsticks (combined) to get the perfect shade I want. That's because I think the shade I want doesn't exist. If you could imagine a rose/plumb/dull pink/light purple color, with just a hint of red...then you are imagining my shade. So I carry these 4 lipsticks around with me in my little make-up bag. They all get old around the same time, since I use all 4 every time I apply lipstick, which is about twice a day. The easy answer is: When the lipstick is flat. When you've used it all up and it's so flat that you can start feeling the round metal ring around the lipstick, that's when it's time to replace....and reload. Lock 'n load. haha
I do not have the habit of wearing lipstick, so I tend to replace them when they become very hard and dry, since they rarely get used. When I smell them, it's smells like chemical already, so I know that it's time for the lipstick to be replaced.